When I start having issues with PVE on a planet that means a couple of things. I have not repaired lately which will cause your stats to go down, you need to upgrade your gear or you are under level for the area. You didn't specify what level or class in your opener.
I have leveled 4 Imp tunes over level 20 and one to 50 and there is not one class quest where I needed help. Yes some were pretty tough and sometimes I would die but call the droid and give it a 2nd go. I seemed to do better when I have a chance to setup for the battle instead of being tossed in the middle of it.
I helped Repub today do his class mission on Tatooine and it was hard for the both of us. We wiped once and I died the 2nd time but he lived and completed it.
The storyline missions for the classes are some of the best I have seen in any game.
In short you are doing something wrong. Yes the elites are tough. Gear up. Stun, knockback and use med packs.
You need to understand what your companions skills are. If you like to immobilize a couple of the mobs then make sure your companions AOE skills are turned off. If you have leveled a bunch make sure that his or her newer skills are actually turned on.
Don't quit ask in game for some help. Join a guild and have fun!