Evade

Evade is a rogue-only ability that becomes available as soon as Hide does, and isn't actually a skill itself, but rather, you evade by using the Hide ability during battle.

To evade, stop attacking then press the hide button.

Upon a successful evade attempt, the rogue will see the message "You have momentarily ducked away from the main combat."

Upon a failed evade attempt, the rogue will see the message "Your attempts at ducking clear of combat fail."

The rogue's success rate is dependent on the skill level of their Hide ability, overcap modifiers from gear decrease the chance of failure.

When to Evade

There's no single time a rogue should use evade. Good rogues evade differently depending on the encounter and tank's ability to hold aggression. Here are some common strategies:

Save it:

Save evade for when the mob turns on the rogue, that way it will always be available for that "Oh sh*t!" moment when the tank temporarily loses aggro. This strategy is somewhat risky as the rogue may have to evade multiple times in a row to lose aggro (because of failures).

After a big hit:

Only use evade every time the rogue land an exceptionally hard hit (e.g., insidious stabs and other critical backstabs), effectively negating large increases in total hate, and preventing the mob from turning on the rogue. This will prevent the mob from turning on the rogue most of the time, but will likely still result in aggro every once in awhile.

Periodically:

Through pure experience the rogue should learn to know when it has been long enough since the last evade, and only evade often enough to keep just below the tanks spot on the hatelist. Ideally the rogue evades just often enough to never steal aggro from the tank but not so often that total dps is lowered by sitting out of combat too often.

Spamming a Macro:

Make a fully-automatic evade macro (see Macro below) that allows you to stop attacking, evade, then begin attacking again all in one button press. Just spam this.

This is the crudest method of using evade, as the rogue will stay much lower on the hatelist than is actually necessary. Each time the macro is pressed the current weapon swing will be rest and overall dps will be lowered significantly if the macro is constantly spammed. An additional drawback is the rogue will always be waiting on the the reuse timer, and evade may not be available for that "Oh sh*t!" moment when the tank, for whatever reason, has temporarily lost aggro.

Tips

Rogues are not tanks and lose a substantial amount of dps every time the mob turns to attack them. Attacking from behind prevents most mobs from using defensive skills against weapon swings (riposte, evade, etc.), not to mention rogues only get max backstab damage from the back. Competent rogues will find the right balance between evading and doing great amounts of damage.

Be patient. When the mob is bouncing between the rogue and the tank, or the rogue just can not seem to lose the mob's attention, it's best to evade and stop attacking. Let the tank beat on the mob for an extended amount of time, before reengaging the target. If the rogue doesn't give the tank a chance to get ahead of on the hatelist, the tank may never get aggro back in time to prevent rogue death (or a substantial loss in dps).

Evading is a good way to get skill ups for Hide.

Pass it on! If you see a rogue that is having a hard time with aggression, they may not know about it (there is no in-game introduction of the ability). It couldn't hurt to mention it nicely. You might actually help them. A lot.

Macro

Rogues can make a simple macro in the socials window that will allow them to evade with just one click:

First open the socials window and right click an empty slot.

Title it "Evade".

For each line add in the following

/attack off
/do # (use the number your hide skill is set to)
/pause 1
(optional) /do # (use the number your hide skill is set to) - this prevents a visual bug that can leave the rogue invisible to other players
/attack on 

Click and hold the slot titled "Evade" to make a hotkey and drop it into your hotbar.

Bug!

Breaking hide by attacking may cause a visual bug that prevents other players without see invis from seeing a rogue that has evaded, this can be prevented by unhiding before re-engaging after an evasion attempt.