I'm less bad than the next guy, and it takes a long time for me to find people where that isn't true.What Makes You a Top DPS Player?
The top DPS players clear the basics: "rotation"/priority, having acceptable lag and PC/network performance.What sort of things are the players who are always first in dps doing differently?
The top DPS players make sure they don't make basic errors, like placing GCD abilities in a macro.
That gets you to the top 10%.
The top DPS players beyond that go to the next level and understand how their damage works. They understand how DoTs work, how chains work, how their buffs and debuffs work.
Understanding these enables the top DPS players to tweak and tune their approach on specific fights to optimize DPS.
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In every fight in the game that's not 100% trivial, there are ways to optimize DPS. Even in ultra straightforward fights like Atomos, as a DRG I will Elusive Jump to the boss. In Titan EX, there are ways to modify your attack sequence to maximize DPS. For example, if you can AOE the gaol + Titan, that is more DPS than just attacking the gaol (as long as the mechanics of killing the gaol do not suffer). If you have an AOE cooldown, time it for that event instead of just blowing it on a single target.
In a fight like Levi or Ifrit, a player who tab DoTs the nails/orbs will get more DPS than direct damage. A player who tab DoTs the nails/orbs in the correct order will get even more damage. A player who partially DoTs the primary nail, then fully DoTs the next objects in the correct order will get even more damage out.
In Leviathan, the melee player who positions themselves to slide into the tail will gain a half or full GCD compared to the player who runs across the platform after sliding.
In Titan, the melee player who times their re-engage to occur right as Titan goes vulnerable after his jump will gain a half GCD compared to the player who waits for Titan to run to the tank.
In Leviathan, the melee player who uses their burst AOE cooldown (Howling Fist, DFD) on the add + Tail will do more damage than the player who just uses the cooldown on the tail or just on the add.
In a fight like Caduceus, if you load up your DoTs on the primary snake when it is low, then switch to the new snake, you will increase your DPS because you have two simultaneous DoTs running.
Another poster mentioned the example of a tank turning a boss. A top DPS melee player can react to it more quickly. They can even predict when the tank will turn the boss. They will also predict when the boss will turn and cast a mechanic. Or, they will time their abilties so that they can mitigate the chance that the boss's turn will screw up their positional attack.
A top DPS player can use a flank attack on a target that is attacking and facing them.
These are just simple examples.
On paper, it doesn't sound complicated. Durr, my AOE is better when I hit more targets. Humm, dotting many things is good.
In practice, being aware enough to be able to execute those things and to do them correctly is uncommon.