If they enemy only has fighters (and not AT or MG or MechInf units that can intercept more then once) then send in fighters first, then your more valuable bombers also works well, their fighter intercepts are sapped by the fighters, and the bombers then get it easy and do more damage.
A great point in the game is if you can get fighters and they only have baloons, in that case you should be able to station fighters close enough to the fight that they cover your ground units, and you can also use some offensivly. It is a great force multiplier as their baloons do very little, and your fighters dominate the sky (and therfore bombardmend).