i'll start with what to buy
empire buy: stormtroopers, at-st, spma-t, 2m-repulser tank, at-at (as many as you can afford), at-aa (not too many), tartan cruisers, victory star destroyers (but try to get normal star d's), imperial star destroyers, interdictor star destroyer (just a couple), tie scout (not too many), the death star
rebels buy:x-wings, y-wings, correllian gunship, alliance assult frigate, mon calamari star cruuiser, rebel soldier, plex soldier, infiltrators (not too many), t-4b tank, t-47 airspeeder (as many as you can get), mptl artillary
turrets are great!
get as many as you can, try to control every build pad
put aa turrets in the middle so that bombers will be destroyed if you're the empire put more aa turrets out to get t-47s
put anti infantry and anti vehicle turrets near each other
if the indigenous people are against you put anti infantry turrets near their spawn points so they die instantly
put smugglers on planets you don't want to conquer strait away