Dragoon Guide/Heavensward
Basic Tips
Dragoons of all levels will want to keep a few basic tips about their skills in mind to help maximize DPS.
Heavy Thrust: Keep this buff up at all times; it's basically a free Raging Strikes. It should always be the first thing you use. If you can tell that it's going to fall off in the middle of a combo, use it again before starting that combo. Remember to use this from the enemy's flank.
GCDs: Until you get to level 26 and unlock Full Thrust, you should be using Impulse Drive all the time and never True Thrust/Vorpal Thrust, since it does more potency on average. But after level 26, Impulse Drive always does less than your Full Thrust combo. Once you get Disembowel, you can start alternating between combos.
Feint: Feint is, in 99% of PvE cases, not helpful. You can get by perfectly well while ignoring the fact that this weaponskill exists.
Keen Flurry: As Dragoons aren't the ones taking most of the damage, you won't be using this skill too often. At lower levels, if you happen to rip aggro on a boss from a tank, it can help out a bit.
Piercing Talon: Later on, this becomes a pretty big TP hog. However, in boss fights when you find yourself having to get far away from the boss, throwing one or two in usually can't hurt.
Recommended Cross-Class Actions
Internal Release is the most important of the cross-class actions for a Dragoon to take, as it is the biggest increase in damage available. Mercy Stroke will also give you some free extra damage near the end of a boss. These are the two actions you always want to have on your hotbar.
The other three choices are mainly a matter of preference, though Featherfoot and Haymaker aren't worth it, even together, and neither Fracture nor Skull Sunder will never be better than the other tools in your arsenal. Some like taking Foresight or Bloodbath for a little bit of extra defense, while others prefer Second Wind for a quick insta-heal or Mantra for party support. None of these are totally required, though.
Endgame Skill Speed
Skill speed is an important stat for a Dragoon to work around when gearing up for the endgame. Ideally, you want your GCD to be anywhere between 2.38 and 2.41 seconds long. This range has to do with both the timing of Geirskoguls and whether or not you're clipping DoTs vs. letting them fall off. This GCD range equates to anywhere from 590 to 652 skill speed.
Endgame Rotations
Your most basic rotation looks like this:
--> --> --> --> or --> --> --> --> --> or
Essentially, you alternate between Heavy Thrust/Chaos Thrust combo and Phlebotomize/Full Thrust combo, weaving in off-GCDs between. Should Blood of the Dragon ever fall off, you can revert to the old 2.0 rotation (nicknamed by some the "rotation of shame") until it comes back up. Instead of going back and forth, you'll be doing Chaos Thrust combo -> Full Thrust combo x2 -> repeat, while alternating Heavy Thrust and Phlebotomize every combo.
Opener (with potion)
--> --> --> --> --> --> --> --> or --> --> --> --> --> --> --> --> --> or
Opener (without potion)
--> --> --> --> --> --> --> --> or --> --> --> --> --> --> --> --> --> --> or
AOE Rotation
Only use your AOE rotation when there are 3 or more mobs, otherwise use your single-target rotation. Doom Spike has a larger AOE than you might realize, but it may still be difficult to line up the enemies; Ring of Thorns is good in those cases. Keep Heavy Thrust up throughout, remember to use Invigorate, and weave in off-GCDs as you go.
General Endgame Tips
Dragoons and TP: Another reason for the soft skill speed "cap" is that higher skill speed drains your TP more quickly. Be sure to use Invigorate as soon as you see your TP bar dip below 500 so that you have it up again as soon as possible.
Battle Litany: These buffs don't stack, so if you have another Dragoon in the party, be sure to ask them if they want first or second. That way, you can have this buff up for double its duration by using them back to back.
Geirskogul: A good way to figure out if you have enough uptime left on Blood of the Dragon to use Geirskogul is to find out your threshold--how low the timer can be right after using Fang and Claw/Wheeling Thrust. At 2.38s GCD, that threshold is 21 seconds. It will be higher the less skill speed you have, so be careful. Also, if Blood of the Dragon (the skill) is about to come back up, you can freely spend a Geirskogul one off-GCD before using BotD again. A lot of Geirskogul usage technique has to do with learning fights well enough to know when you may want to save Geirskogul or manipulate the BotD in a certain way.
Blood for Blood and Chaos Thrust: Try to make sure you have the first up for the second, as Chaos Thrust's damage over time effect makes up a large portion of your damage. It's hard for them to miss each other unless you use Blood for Blood literally right after Chaos Thrust, so try not to do that.
Power Surge: Always pair Power Surge with Jump, since it has more potency than Spineshatter Dive. Ideally, every sixty seconds you want to use the two in back-to-back off-GCDs.
Life Surge: You don't need to wait to always use this on Full Thrust. If it's up and you're about to use Fang and Claw or Wheeling Thrust, and you know you'll be able to hit the positional on it, go ahead and use Life Surge--you're actually losing DPS by saving it for later.