Implements:

For example, in the PHB1:

Clerics make use of holy symbols to help channel and direct their divine powers. A cleric wearing or holding a magic holy symbol can add its enhancement bonus to the attack rolls and the damage rolls of cleric powers, as well as cleric paragon path powers, that have the implement keyword. Without a holy symbol, a cleric can still use these powers, but he or she doesn’t gain the bonus provided by the magic implement.

The Holy Symbol acts as the Priest's "implement" and any attack power with the implement keyword gets to add their implement enhancement bonus to attack AND damage rolls. 

For example, in the attack power "Hellish Rebuke" for the Warlock:

(insert image)

 It lists "implement" as a keyword. For Warlocks, implements can be wands, rods, or certain types of daggers (such as a pact dagger). If the Warlock is brandishing a +3 Rod of Awesomeness, they get to add that +3 to their attack and damage rolls. 

So if your character class attack powers get the benefit of an implement, be on the lookout to purchase and/or acquire the implement that is right for you!

Lights, Camera, Action Points!

From the PHB1:

Once per encounter, you can spend an action point.
When you spend an action point, it’s gone, but you can
earn more.

✦ You start with 1 action point. (Monsters usually have no action points.)

✦ You gain 1 action point when you reach a milestone (page 259).

✦ After you take an extended rest (page 263), you lose any unspent action points, but you start fresh with 1 action point.

✦  During Your Turn: You can spend an action point only during your turn, but never during a surprise round.

✦  Gain an Extra Action: You gain an extra action this turn. You decide if the action is a standard action, a move action, or a minor action.

✦  Once per Encounter: After you spend an action point, you must take a short rest (page 263) before you can spend another. (Some monsters can spend more than 1 action point per encounter.)

The choice of what  action you decide to take (a standard action to use another attack power, or a move action to tactically place yourself within the battle) can be crucial to the outcome of the combat. Do I spend my Action Point to use an attack power that helps the NEXT player coming up to fight? Do I retreat? Do I deliver a devastating Coup-De-Grace? The choice is yours!

Targeting What You Can't See 

Invisible Creature Uses Stealth: At the end of a concealed creature’s turn, it makes a Stealth check opposed by your passive Perception check. If you beat it, you know
there’s a creature present that you can’t see, and you know the direction to its location. If you beat it by 10 or more, you know exactly what square the creature ended its turn
in. The concealed creature also makes a Stealth check if it takes an immediate action or an opportunity action.

Make a Perception Check: On your turn, you can make an active Perception check as a minor action, comparing the result to the concealed creature’s last Stealth check. If
you win, you know the direction to the creature’s location, or its exact location if you beat it by 10 or more.

Pick a Square and Attack: Choose a square to attack, using whatever information you’ve gleaned so far about the target’s location. Roll the attack normally (taking the –5
penalty for attacking a creature that has total concealment). If you pick the wrong square, your attack automatically misses, but only the DM knows whether you guessed the wrong square or your attack just missed.

Close or Area Attacks: You can make a close attack or an area attack that includes the square you think (or know) the concealed creature is in. Your attack roll doesn’t take a penalty from the target’s concealment.

A Breath of Fresh Air - Second Wind 

Second Wind: Standard Action

• Spend a Healing Surge: Spend a healing surge to regain hit points.
• +2 Bonus to All Defenses: You gain a +2 bonus to all defenses until the start of your next turn.
• Once per Encounter: You can use your second wind once per encounter and can use it again after you take a short rest or an extended rest. Some powers (either yours or another character’s) allow you to spend healing surges without using your second wind.

Dual Personalities - 4e Multi-classing 

Multiclassing means being two different classes at the same time. This provides benefits like opening more options for Paragon Paths and feats, and giving you access to powers from the second class. Your primary and secondary classes are not equal - it's more like you're dabbling in the secondary class than splitting between the two. The number of feats you spend toward multiclassing and the choices you make affect just how heavily or lightly you delve into the second class.

Multiclass Feats

The way to multiclass is to take one or more of the eight Multiclass Feats listed on page 208 of the Player's Handbook. Taking one of these feats causes you to technically qualify as both that class and your original class. For example, if you're a warlock and you take the Arcane Initiate feat, you are now both a Warlock and a Wizard and satisfy the Wizard requirement of feats, paragon paths, epic paths, etc.

There are two big restrictions here: First, you cannot multiclass into your own class (no double dipping for repeat benefits, so a Fighter can't multiclass into Fighter). Second, you can only multiclass once, so you can dabble in one additional class but not two (although the epic path Eternal Seeker is a way to dabble in many classes fairly freely).

Note: Multiclass Feats are different from Power Swap Feats, which are described below.

Multiclass Benefits

(or rather, "What's the point?")

In addition to being two classes at once for bragging purposes, you get the following benefits:

• You can take any Feat, Paragon Path, or Epic Path for the new class.
  • This means you could take any Wizard paragon path as a Warlock (for example, Blood Mage or Spellstorm Mage), or any Fighter paragon path as a Ranger (for example, Pit Fighter). If a paragon path from another class interests you more than what your class offers, this 1 feat will open it up to you.
• You gain free training in 1 skill from the class you multiclass into, as though you took the Skill Training feat. For some classes, this is a specific skill (Arcana for Wizard, Religion for Cleric, Thievery for Rogue). All other classes let you pick any skill that is a Class Skill for that class.
  • This means multiclassing can often be better than taking the Skill Training feat if you can meet the requirements, because you gain training plus extra benefits.
• You gain limited use of 1 class feature from the new class. If it's an at-will power, you can use it as an encounter power. If it's an encounter power, you can use it as a daily power. This isn't the greatest power in your arsenal, but it's a nice perk.
  • Multiclass Ranger, for example, lets you use hunter's quarry once per encounter. Warlord and Cleric let you use their Inspiring Word/Healing Word once per day.
• If the class uses implements, you will gain the ability to use this implement when using the new class's abilities.
• You can take the Power Swap Feats on page 209 of the Player's Handbook (explained below).

All of the above is provided with only 1 feat. If you have more feats to spare, the power swap feats may interest you.

Power Swap Feats

The "Power Swap Feats" let you choose some power from your primary class that you're not ecstatic about and swap it for another power in the new class that's cooler. There are 3 power swap feats, each requiring you to be a specific level before you can take them:

• Novice Power (level 4): swap one encounter power
• Acolyte Power (level 8): swap one utility power
• Adept Power (level 10): swap one daily power

Each power swap feat lets you toss out one of your powers of a specific type and grab a power of the same type of equal level or lower in the new class. So if you didn't like the level 6 Warlock utility spells, you could grab a level 6 or level 2 Wizard utility spell instead.

Notes:

• Even though you have to be a certain level or higher to take these feats, you can use them to swap powers of any level. Adept Power lets you swap any daily power of any level from your primary class for any daily power of the same level or lower in your secondary class.
• You can only do this with 1 power per swap feat, but every time you gain a level you can change your mind about which powers the feats apply to. Basically you undo the swap you did when you took the feat and decide again. This isn't just for undoing mistakes -- if something better becomes available as you level up, you can grab it instead.
• Paragon and Epic path powers are not swappable through these feats.

Examples:

Example 1:
You are a Warlock who has multiclassed into Wizard. You take Novice Power at level 6 and decide you want to swap your level 3 warlock encounter power for a level 3 wizard encounter power. You decide upon Icy Rays.

Example 2:
You had swapped a L6 warlock utility spell for a L6 wizard utility spell, but found something you liked better when you leveled up to level 10. You decide to undo your previous decision and grab the higher level power instead. You get your L6 warlock utility spell back and lose the level 6 wizard spell, and then trade out your L10 warlock spell for the L10 wizard spell you liked.

The only restrictions are that you can't swap out powers from your paragon or epic path, and you have to swap for a power of same level or lower.

Swapping Your Paragon Path

There is one final perk to multiclassing. If you take all 4 multiclassing-related feats (the multiclass feat and all 3 power swap feats), you can decide to not take a paragon path at all. If you do this, you get the following benefits instead:

• At level 11, you can choose to swap one of your class's at-will powers for an at-will power from your secondary class.
• At level 11, instead of gaining the paragon path encounter power, you can choose any encounter power of 7th level or lower from the new class.
• At level 12, instead of gaining the paragon path utility power, you can choose any utility power of 10th level or lower from the new class.
• At level 20, instead of gaining the paragon path daily power, you can choose any daily power of 19th level or lower from the new class.

Summary

In summary, multiclassing gives you:

• Access to feats, paragon paths, and epic paths that require the class you multiclass into.
• Free training in a skill, often of your choice from the class's Class Skill list.
• Limited use of some class features from the new class.
• Access to 3 Power Swap Feats to trade powers between classes.
• The ability to trade your paragon path out completely for more powers from the new class.

And that's all there is to D&D4 multiclassing. If you want to branch out further (or branch out without having to multiclass), Eternal Seeker is an ideal Epic Path.

 "Role"-Playing - Knowing Your Place

Controller:

The Controller role focuses on dealing a lot of damage to as many enemies as possible, or to hinder their progress. This makes monsters easier to kill by the other members of your party.

Defender:

The Defender role focuses on dealing out damage to enemies while keeping them from reaching or harming allies. Defenders are often challenging to get past or even to move away from.

Leader:

Leaders inspire, heal, and aid the players. Leaders generally have good defense and attack, but their true power lies in boosting the power of their party by healing or buffs and hindering their enemies by weakening them.

Striker:

Strikers specialize in dealing high amounts of damage to a single target at a time. They have the most concentrated offense of any character in the game. Strikers rely on superior mobility, trickery, or magic to move around tough foes and single out the enemy they want to attack. 

Teaching Old PC's New Tricks 

Sometimes you make decisions when you create or advance your character that you later regret. Perhaps a power you chose isn’t working with your character concept, or a feat never comes into play the way you anticipated. Fortunately in such a case, level advancement isn’t only a time to learn new powers—it’s also an opportunity to change some of those decisions. Every time you gain a level, you can retrain your character: change one feat, power, or skill selection you made previously. You can make only one change at each level. When your class table tells you to replace a power you know with a different power of a higher level, that doesn’t count as retraining—you can still retrain an additional feat, power, or skill as normal.

Feat: You can replace a feat with another feat. You must meet the prerequisites of the new feat. You can’t replace a feat if it’s a prerequisite for any other attribute you have (another feat or a paragon path, for example), or if the feat is a feature of your class, path, or destiny (as the Ritual Caster feat is a class feature for wizards). You can replace heroic tier feats (see page 193) with higher-tier feats, but only one at a time, once per level you gain. For instance, at 11th level, you gain one feat and you can also retrain one of your heroic tier feats, gaining a paragon tier feat in its place. At 12th level you can do the same, so you can potentially have four paragon tier feats at 12th level. (You might find that many of your heroic tier feats remain worthwhile well into higher levels, however.)

Power: You can replace a power with another power of the same type (at-will attack power, encounter attack power, daily attack power, or utility power), of the same level or lower, and from the same class--a 5th-level attack power for another 5th-level attack power, for example, or a 22nd-level utility power for a different 22nd-level utility power. You can’t replace a power that’s a class feature (such s a cleric’s healing word or a warlock’s eldritch blast) or  power gained from a paragon path or epic destiny.

Skill: You can replace a trained skill with another trained skill from your class list. You can’t replace a  kill if it’s required for a feat, a power, or any other  attribute you have, or if it’s predetermined by your class (such as Arcana for wizards or Religion for clerics). If your class requires you to choose one of two skills (such as the ranger, which requires either Dungeoneering or Nature), you can alter your choice by retraining, but you’re limited to replacing one skill with the other.

Marky Mark & The Adventuring Bunch 

From the Essential Rules Compendium:

"When you mark a creature, you force it to engage you or suffer the consequences. While that creature is marked by you, it takes a –2 penalty to attack rolls for any attack that doesn’t include you as a target. In addition, powers, class features, magic item properties, and feats might have effects that trigger when the creature takes certain actions.

A creature can be subject to only one mark at a time, and a new mark supersedes a mark that was already in place. The effect you use to mark a creature determines how long the creature remains marked by you. Regardless of the mark’s duration, it ends if someone else marks that creature, unless an effect says otherwise."

Feats/Class Features/Powers that allow a mark to to not be superseded by another are rare, but they do exist. Some resources for this are the Martial and Divine Power source-books.

Also, be aware how your marking mechanic functions for a specific class. For example, from the PHB1:

"Once per turn as a minor action, you can place a Warlock's Curse on the enemy nearest to you that you can see. If you hit a cursed enemy with an attack, you deal extra damage.You decide whether to apply the extra damage after making the damage roll. You can deal this extra damage once per round."

 Once per round means that, in the case of this example with the Warlock, should the player apply the extra Curse damage to an attack, then utilize an Action Point, or some other method to gain an additional Standard Action to preform another attack, they cannot apply that Curse damage to another cursed enemy within the same round. 

A similar situation arises with the Paladin's Divine Challenge, from the PHB1::

"The marked target takes radiant damage equal to 3 + your Charisma modifier the first time it makes an attack that doesn't include you as a target before the start of your next turn."

The Divine Challenge does it's damage once per round, just like all other marks (Warrior Mark only allows one attack). If you can mark multiple targets, it'll pop all of them. Another example is he Combat Challenge feature of the Fighter from PHB1:

"Every time you attack an enemy, whether the attack hits or misses, you can choose to mark that target. The mark lasts until the end of your next turn.In addition, whenever an enemy marked by you is adjacent to you and shifts or makes an attack that does not include you, you can make a melee basic attack against that enemy as an immediate interrupt."

Also note, that an Immediate Interrupt uses an Immediate Action, which you only get once per round.

 Let There be Light!

Light in 4e is very simple, you have 3 types of light - Bright, Dim and Darkness.

In Bright light, there are no penalties.
In Dim light, everything has Concealment against creatures with Normal vision. (-2 to hit)
In Darkness, everything has Total Concealment against creatures without Low-Light vision. (-5 to hit)

That's it.