Star Wars: Empire at War Hints for PC
Unlike many games, you can't send small forces numerous times to weaken the enemy. It would be easier to build your forces and use them all at once. If losing, just retreat, build, attack again.
Its really easy, all you need to do is when you capture planets, Just build mining facilities on them until you get about $15,000 a day. After a while, you will have heaps of money.