Are you trying to solo heroic areas?
Heroic areas are group agreas, where mobs(enemies) are all strong/elites/champions, most of these are very hard or impossible to solo and they will kill any normal player easily and quickly.
In pve you should always start a fight with ctrl-1 and make sure Khem is targeting the strongest enemy. While he is beating on the mobs, you should cast your shield on him and heal him if needed, while you kill the weakest mobs.
You can also use whirlwind(CC = crowd control) to stun strong mobs for 60 seconds, while you kill others first. Remember that if Khem is fighting close to the stunned mob, he will usually break the stun, because of his area of effect attacks. You can disable his AOE attack in the companion bar, I think it's called "Cleave," if you are in a situation where you use whirlwind alot.