Build at as many places as you can, X-Wings for space and Infantry Platoons or Plex Soldiers for land. Since X-Wings have such a high fire rate, they will kill enemies easily. When the space battle is over, take the ground with your forces. It may also help to have some T2-B Tank squadrons. With the Plex(s) as high defensive and your platoon(s) doing the rest, you should win quickly. This will also work for Galactic Conquest mode.