In the thick of battle, do not forget about Smoke Screen. Use it on a high-dps class that is targeting you to reduce the damage you are taking from them. Make sure that you do not hit the target that you cast Smoke Screen on, lest you completely negate its effect.
Your other clutch defensive ability is Cauterize. Its effect is entirely erratic, removing a single, random negative effect from you, but it can, and does, save your life if you use it as often as possible.