Play as the Empire, and instead of only using force (troops, TIE's, ect.) use diplomacy. The planets will stay loyal better when they are politely convinced to join your cause. However always leave garrisons on core planets so the rebels can't just land and capture them, I typically use Clone stormtroopers and TIE Interceptors as garrison troops. Download the RebEd program and you can alter characters stats to be more diplomatic minded, also Rebed allows you to load different "cards"-characters , troops, ships, ect. It really is a great program. Any other questions or thoughts, just ask.- Grand Moff Conway