Well, if it's outside Echo Base, use the AT-AT to move between the CPs, and kill alot of the rebels as you move. When you get to the CP, an AI bud will usually be right behind you to take up the AT-AT, so he'll likely tie up most of the rebels.
To take out the Sheild generator, use an AT-AT.
To take Echo Base, wait till sum buds come up. The rush in and hide behind the service tower thing in the back behind the CP.
To finish the last part, Vader run to the point. Then move around to dodge the grenades, and saber throw. If you do it well, you'll saber throwing will kill them before they can throw their grenades.