In the mission on Tantive IV (blockade runner), the first and final objective are very difficult. At the start, once the door explodes and opens, use your thermal detonators. Get to the CP and keep dodging bullets and firing while standing near the CP until it is turned to your faction. This may take a few attempts, but it will work. Use Darth Vader after you have captured it. Use a regular Stormtrooper to take care of Leia. She should be around where you started the level. Use your grenades to soften her up, then your rifle to finish her off.