Wow has nobody really posted in Illusionist yet? Well here it goes...
PVP Illusionist!!! Some people consider this to be THE #1 pvp class. mainly due to the CC they can provide.
Illusionists are good at both TW, 1v1 and 3v3
TW
The key to a TW illusionist is always keeping up your buffs and always spamming your attacks (Fireball vs Icicle is highly debatable >.<).
Stimulation + Mind Surge can keep your entire group topped out and dealing a lot more damage than they could without it. While you do have to slow down your personal dps to do this (not by much) it will be worth it as crystals are decided by cumulative DPS.
Usually the opposition won't be a problem but if they are (Eminence...) then you should be sleeping them around the crystal occasionally.
1v1
1. Invis (Psionic Focus)
2. Sleep
3. DoTx3
4. Deadly Icicle
5. Kite or just kill
Always OP and self explanatory. Against knights its a different story as they can't be slept. Just try to kite them around with your DoT and burst them down. They're the hardest matchup for the Illu. It's not like 1v1 matters anymore anyway though xD.
3v3
This requires team coordination. With a proper team I've won fights that I never should have been able to win (ex. 45, 55, 40 vs 55,51,52).
Coordinate with your team to see who's the biggest threat. Make sure to sleep all the others except the biggest threat and coordinate with your team to just focus him down. While it might seem like a good idea to focus the healer generally by sleeping the healer and killing off the dps fast then there is a much larger chance of winning.
Ex. 55 Healer, 55 DPS, 55 MDPS: Sleep the healer + one of the DPS.
As always keep stimulation and Mind Surge up, it does help. Tele away if threatened etc.. Don't worry if you miss your sleep. Just keep casting until you sleep who you wanted to.
REMEMBER: Team coordination is key. If they just run in and AOE your sleep will be useless.