An easy way to beat the At-St is to stay directly under it, and keep facing up and shooting it. His percentage will keep going down and you won't get hurt! But be careful to always stay directly under because he moves around a lot looking for you.

Another helpful tool to use in the Imperial Sewers is to turn the brightness up on your set to see much better.

In the speeder level it is easiest to beat the speeders by slowing down when you meet one and just keep banging it into the wall. If you stay calm you can kill all of them in the city. And if you stay side ways in a underpass they will turn away and crash.