Here are some very practical tips on Abyss PVP for those who have no experience of it in Aion, the information is given by MidnightTempest . Please have a look and have a good time here!
1. Items Needed for Abyss PVP: HP pots, mana pots, resurrection stones, the yellow potion which cancells out any abnormal status, flight scrolls to increase your flight time, and speed scrolls to increase your movement speed by 20%, useful to chase down running enemies or to escape.

2. A common mistake that many newbies make is to drink HP (buy with Aion gold ) potion only when their HP is low. The correct tactics is to drink potion as soon as the damage inflicted upon you is equilavent to what the potion can heal. That way when the cooldown for the potion is over, you can drink another potion again to recover your HP.

3. Watching the skies on top of you is more important and practical than watching the ground around you in the Abyss. 90% of enemy faction's ambushes come from the skies.
4. If you need to rest after a fight to recover your HP and MP, always rest on tree tops. Resting on the ground in Abyss makes you a sitting duck in a shooting gallery.
5. Templars, Clerics and Chanters may like to brag about their multi-tanking abilities, but in reality it's very difficult for any class to win in a 1 vs 2 situation: unless you have far better equips and 4+ higher levels.
6. In a large scale group PVP, forget about choosting which enemy to target, it's often too hectic and chaotic to make a good decision, and you will likely die before you can make up your mind. It's better to press TAB and attack the nearest enemy while you are still alive.
7. Use the movement bonuses, they really do work. Sorc, Spiritmaster, Ranger, Glad are recommended to move forward to get the damage bonus. Templar, Cleric and Chanter are suggested to move backwards for the defense bonus, while Assasin should move left and right for the evasion bonus. Of course, it also depends on what the particular situation requires.

The source is . I hope it can be useful.