Backpedalling can be an effective way to lure a dpser away from a target as they will think your are a real noob and come after you. As a tank you will take a while to kill one on one if you are not ambushed, whhc gives your mates time to assist.
Use your taunts to help knock down the damage the enemy is doing to your mates. Guard.
Get a programmable mouse (I just got a Razer Naga and am learning to use it) it will help.
Using the mouse to move is key. It takes practice, so go some place where you can without much danger of death and do that.
Situational awareness comes with experience. Stay near a healer except when you have to go in and be spoiler.
Retractable blade is a good way to put a dot on stealther and they don't like that.
Keep learning and hang in there. I started out with a tank build, but I switched to Advanced prototype for PVP and I like it a lot. Mobility adds to your chances of survivability, whihcs means more time doing damge and less in the box waiting to get back in the fight.
Use your stims!
Stand right on the edge of platforms, fire and acid when you can, facing into it, and grapple the enemy into the mess then stun them. Standing on the edge of a platform can casue leapers to fall after they jump to you. Hilarious!
Practice and tune your gear and build as you learn.
Good luck!