Sgt Shorzen killed my Lvl 42 Vanguard Trooper at least 10 times before I beat him. Kudos to anyone who beat Shorzen while at a lower level!
There have been lots of good suggestions about battle tactics here, I'd just like to add my technique.
How do you use your keyboard & mouse to fight? I know lots of players use the number keys to select an attack, but I find it slows me down to do that because I'm looking from kybd to screen while choosing an attack. When I'm fighting, I barely look at my opponent. Instead, I use my A, S, D, & W keys to dodge his attacks, and use the mouse to select an attack from my abilities bar. This helps enormously in monitoring cooldowns on various weapons, as well as being able to easily monitor my opponent's and my health levels during a fight .
That said, I still couldn't beat Shorzen until I bought a med pak at Fleet that gave me up to 3375 health points when I finally used it. I pretty much let Tanno Vik do his own thing without interfering with him while I attacked. I still found it necessary to get out of Shorzen's weapon reticle when he was about to firebomb me, that firebomb is devastating. This method of fighting let me and Tanno both survive our final battle with Sgt. Shorzen.