Positioning does help prevent you getting knocked off a lot less often. Sometimes you will get knocked off, it happens to everyone. Put your back against a beam, another object, or line yourself up with platform you are on, so you land on it again.
Slow the person while you are on them. This should allow your charge to come off cooldown so you can start bashing them again. If you are getting hosed while you are on the ground use your abilities to minimize the damage. You have 4-5 to choose from so something should be available.
Do not forget about the health bonuses laying around either. I eat these things like candy.