What's your build and rotation?
I have to admit I have doubts.
I'm assault, and I generally stay alive by kiting and breaking LOS as needed.
The opening single target burst is basically what everyone does: IR -> AP -> SG -> HIB -> reserve powercell -> full auto -> HIB. Only thing of note slightly different from others.... I almost never stand still, so I never use charged bolt. I only use pulse cannon and mortar valley in very opportunistic situations (no one is hitting me but bad guys are clumped). I think its a waste of ammo. Id rather spam hammer shot. And I *only* use tech override in conjunction with concussion grenade as another immediate escape CC.
In general, when I am targeted by ranged channeled DPS, I play LOS with them. They have all the issues gunnery commandos have. If I'm hurt, I'll regularly duck out of sight and self heal. (I'm talented in the combat medic skill that cuts medical droid time.)
When I'm targeted by melee, it's all about kiting. You can't knock back many juggs after they jump, so cryo, stock strike, and move. AP/SG/IR while moving. If they use cc breaker, use tech override / concussion, and move > 10m away before opening fire. If they slow you, fine, you have a head start and can slow them too. And when they get real close, up goes reactive shield, etc, etc.
Like I said earlier, shadows and sentinels are two classes I have more difficulty with. They have too many defensive CDs that make it so I can't hurt them at the open, and then they can keep me locked down / from escaping with roots + added speed, etc. Oh, and powertechs are still problematic but less so after 1.4. Name of the game there is to do everything you can to keep range > 10m. If they grapple me, it's immediate cryo, and make a run for it. (And cleanse since you're inevitably on fire.)