The key is the use of bombers
. Bomber and fighter squadrons are fairly easy to afford and a large force can be maintained easily seeing as virtually every planet can strengthen it...
Could even throw in some marauders for anti-fighter support, and try saving up for a few strong units to base your formations around, namely Calamari cruisers.
3 x MC
2 x MC30
3 x Marauder
10 (?) x Y and X Wing
Depends on your unit cap of course. I sometimes forget mine is set to 60 for the Rebels.
Just try out logical combinations.