Last edit 17.04.2013.
If you just have experience with normal-PvE enemies your first experience in dungeons can be extremely devastating. Goal of this guide is to give you as smooth crashing as possible.
First of all, read the wiki-page for dungeons and fractals!
Dungeon-specific guides you can check here.
Please ask if you have any questions/concerns. It's quite hard for me to know how new players see dungeons.
Prepare your character
If you are playing your first character I seriously suggest reaching level 80 first. This gives you time to learn the game. You get downscaled in lower level dungeons but additional traits and access to rare/exotic gear make a difference. Also being a level 80 helps finding a group easier.
Get best gear you can afford from Trading Post (or craft). Compare different options and pick suitable one for your budget (like level 80 rare, level 78 exotic or level 80 exotic).
At first glance amount of different options may seem devastating (image of different options by Gorani). Try think what stats you want to focus on to narrow choices down (do you need more health/armor? do you focus on raw damage/condition damage?).
If you are completely clueless and have no idea what you are doing I suggest getting level 80 rares with Knight-prefix (toughness, power, precision) with orbs of choice.
Also it is good to carry different weapons with you. This gives variety and allows you to experiment if you run into problems (like some situations greatly benefit from anti-projectile skills). Most importantly have at least one ranged and one melee weapon because there are some situations which greatly favor other one.
Your build is also important. Try focus on party-wide skills, damage and active defenses (evades, block). Scroll down for more detail about game mechanics.
You can use food consumables and "other" consumables (potions, oils, sharpening stones) simultaneously.
Get best food and "other" consumables you can afford from Trading Post. Simple stat-buff or life-steal on critical are good options for food. Get different potions against different enemies but don't forget stone/oil for other situations.
PvE consumables can not be bought from Trading Post. Instead there are NPC's scattered all over the world. (Dulfy has useful guide) Quite many won't work on dungeons!
If you going to join random team you really should read text guides and/or watch videos before-hand. You want as smooth run as possible because most teams disperse after few failures (or simply kick you). Also you can't rely them to guide you properly (or at all).
This site has text guides but feel free to use your favorite search engine to look up for other sources (videos).
If you are going with friends it can be extremely fun to figure stuff by yourselves.
Finding a group
Where to get people
Finding a group can be extremely easy or hard. You have 3 different ways to get party members. Most importantly use your contacts and try get guildies and friends to join you!
If you can't fill your group your best bet is to post on lfg-site (http://gw2lfg.com/). If even this fails your only option is to start spamming "lfg" in Lions Arch or in dungeon entrance.
Joining existing parties
If you want to join an existing party you need to be aware of its requirements. Parties can be looking only level 80 characters, only character with exotic/ascended clear, only players with previous experience or specific classes. If you don't meet their requirements your options are talking your way in or lying. If you lack gear, level or class you can try make it up with your experience. If you lack experience you can try make it up with gear and willingness to listen. "Experienced" people aren't usually that good so if you have read guides/watched videos you can quite easily claim that you are "pro".
On the run
Calling targets is a powerful tool because it allows your party kill an enemy faster which reduces enemy pressure (and ensures progress). Often teams don't use because it's not needed. However if your party has issues you should start calling targets. Sometimes 2-3 people call targets which confuses everyone so decide dedicated caller if needed.
If you are in a random group you will very likely heard word "skip" (or just see people running past enemies). People do this because running is often easier and faster while killing has poor rewards. This is often very chaotic and you can expect zero support from your party (if you get downed no one comes for you). So be ready to equip different weapons/utilities on fly if party suddenly starts running.
If you want to skip you should discuss it with your party before running in to make sure everyone is ready. When you get more experienced you should try to make sure that everyone makes it. If one guy dies and resurrects at a waypoint, ask if he needs help. Waiting for one guy to make it can take much longer than if you had killed the enemies.
Exploiting bosses is currently very popular. You may notice people jumping to weird places while bosses just helplessly stand still. This can put you in extremely tricky situation if you want to do it normally. If your actions make it harder for your party you risk getting kicked. If possible you should try to learn these encounters normally (usually faster).
Pulling has two possible meanings. You can pull entire groups to choke-points for better area-damage. However more often it's used to split enemy groups so you don't have to face so many enemies at same time. Enemies often have different leash-ranges/areas (when they start running back). Hit one enemy from max range, run back and hope that only few of them follow/remain!
When people get downed it should be your top priority to get them up. Whether you try to revive or rally them is situational. If there are any low targets you should try to kill them, otherwise try to revive. If you get downed try to tag low health targets for quick rally!
If you get defeated you can't resurrect at a waypoint while any party-members are in combat. Most of the time you should wait for resurrection. If you are in a bad spot (like middle of enemies) you may have to go back to a waypoint.
In Fractals there are no waypoints. Instead there are automatically updated checkpoints. If whole party dies you can resurrect at latest checkpoint.
Eventually you will face the inevitable and see your whole party eating dirt on floor. Many groups tend to just mindlessly retry and retry until they get frustrated (and quit). You should try to analyze what went wrong. Talk with your party, use combat log and just generally try to figure out what got you killed. If you think there's a issue inform your team (be polite, generally people don't like being told that they suck) and try to work on it.
The way game and dungeons are built favor some mechanics. It is important to know which mechanics to focus if you want to be effective. If you lack basic knowledge (what Conditions or Boons check out wiki for relevant articles.
Damage versus Defense
Most important thing to realize is that higher damage also means better survivability. Faster you kill enemies, less time they have to hurt you. However, it's not that simple. You need to have enough defense to survive, if you die all the time you are not dealing any damage. Also if your party-mates deal low damage fights may last longer than expected!
But it's good to keep in mind that higher damage means faster clear times which means higher reward/time.
Point is, build as offensively as you can, keep just enough defense to survive (needed defense gets lower and lower when you get better). If you find surviving easy get more damage and vice versa (optimal if you have two armor-sets). Dungeons have been soloed on glass-cannon (minimal defense) builds so it is definitely possible.
Raw damage versus Condition damage
Raw damage is easier, has less risks and often even better than Conditions. First of all, raw damage has no caps, if enemy hits Condition-cap you aren't dealing any more damage. Also Conditions won't work against Structures and some enemies have immunities/dispels. Finally raw damage benefits from more sources (more stats, Vulnerability).
Condition-build works and can deal major damage but you need to be aware of its limitations.
These are one of the strongest type of skills in the game (against ranged enemies). Enemies are dumb which means one skill can negate lots of damage (or even deal it back in case of Reflection).
If your class has access to AoE anti-projectile skills remember to use them in right spots (Reflections can deal 100k++ damage in some cases).
Avoiding damage versus healing
Generally monsters hit hard in dungeons. This means avoiding damage (evades, blocks, anti-projectile, control) is much more effective than passive tanking/healing (Regeneration, Protection, Toughness, heals).
If you have issues with surviving try get access to Vigor, blocks, etc. Bunker-builds work poorly and just slowdown the group.
It's also good to realize that blocks and evades have a difference. Some attacks can't be blocked (also some attacks can't be evaded either). Single-blocks are weak when damage comes in multiple (small) packets like ticking AoEs, evading avoids all.
Unshakable & Defiant (on bosses)
Most bosses have Unshakable. This means Blind only works 10% of time, Weakness/Vulnerability expire twice as fast and interrupting grants Defiant-stacks. Defiant-stacks prevent interrupts. You need to burn down stacks by wasting interrupts. Once stacks are down boss can again be interrupted once.
Obviously this severely hurts Blind- and control-skills. Interrupting is still useful (self-heals, extreme attacks) but it requires good coordination. Also you may have to consider whether Weakness/Vulnerability are worth of it (mainly utilities).
Summons, minions and pets
While these are great to soak up damage you need to be aware of their biggest issue. There are many cases when you want to avoid enemy attention when sneaking through (skipping) or trying fight a small part of a big group. Artificial intelligence tends to rush in and aggro everything from left to right.
Rangers can't get rid of their pet so they need to be extra aware and control it accordingly.
Using my other guides
If for some reason you have decided to use my other guides this section might be helpful.
Explaining terms used on skill listing (I'm still experimenting so may not be accurate).
Damage: Listed damages are based how much damage my Warrior took (with potion 8-10% damage reduction and with no extra vitality/toughness). Fatal > 200%, Extreme > 75%, very high > 50%, high > 25%, medium > 10%, low > 1%, very low > 0%. These values of course vary based on your health and armor.
Melee: Short-range cone-attack (hits 3 targets). Some might be single-target (please let me know).
Cone: Medium-range cone-attack.
Ranged: Ranged attack which doesn't get affected by anti-projectile skills. Usually instant travel time. Requires line of sight.
Projectile: Ranged attack which gets affected by anti-projectile skills. Projectiles have various travel times. Zig-zagging/side-stepping can be used to avoid slower ones. Anti-projectile skills behave bit differently and there are some exceptions (please let me know). Requires line of sight.
"Some text": Explains animation (etc) of the attack to help you recognize it.
Dash/Leap: Mobile melee-skill. Single-target by default.
Single-target: Used with "Melee" to specify that attack hits just one target.
Bouncing: Used with "Projectile" to specify that projectile jumps to nearby targets. Bouncing attacks can be extremely dangerous if it keeps bouncing between two targets.
Returning: Used with "Projectile" to specify that projectile returns to caster after reaching certain range.
Homing: Used with "Projectile" to specify that projectile follows moving targets.
Trap: AoE which triggers when walked on.
Numbered attacks: Attacks-chained are listed with increased numbers (like Chop (1), Double Chop (2)). Often enemies continue chain if previous attack hits, in some cases they keep going regardless of success.
Basic attack: Means most commonly used attack.
PBAoE: Point-Blank Area of Effect. Centered at caster.
AoE: Area of Effect. Effect applies on specific area and may hit multiple targets.
Ticking: Used with "AoE" to specify that AoE hits over time.
Channeled: Attack lasts over time and needs to be casted.
Aura: Ticking PBAoE which follows caster.