Listen to Innominate, he's got some pretty good tips there. Last tour I flew the A-20 quite a lot in the attack fighter role and was quite successful in it. I also posted a thread with some fighting tips in the Training/Help boards,
A-20 fighting tips.
It's best to carry the max payload for the A-20, 8x 500 pounders. With that payload, there is no town you can't bring down by yourself. The plane is pretty tough too, it can take a beating and still get you home. A lot also under-estimate its fighting ability. Even with a full load of bombs, the A-20 can be quite a handful. It has the ability to fight its way to and from the target with some reasonable expectations of survival.
The A-20 is best used as Innominate said, a low altitude attack plane.
It doesn't have a level bomb sight, so you have to dive bomb your target. Shallow dive bombing works well with minimal risk of yanking your wings off in a dive. You just have to be careful you don't pickle too low or you risk the bombs not arming and failing to go off, or you might get caught in your own bomb blast.
It is also pretty accurate in the dive bombing role. If you go in for a steep dive run on the target, you have to be careful that you don't pull to many G's on pull-out or you'll rip off your elevators. It's best to start your dive at around 225-200mph and keep the throttle cut back in your dive. As you pull out, feed it some throttle and gently pull back on your stick, don't pull more than 3 G's or you'll kiss your two elevators goodbye.
Once your bombs are gone, you've got one deadly fighter on your hands that is more than a match for some of the fighters in the MA. It will out turn planes like the Spitfire Mk IX. The A-20 has a fantastic flat turn rate at 225mph-200 (the best fighting speed for the A-20). It's best to try to keep your plane at 250-200mph to take advantage of its turn rate. The flaps don't deploy until 200mph but you'll find yourself using 1 or 2 notches of flaps and some times not at all. It is also a decent stall fighter for a plane of its size.
The top turret is basically useless if you are self-gunning. The fields of fire are so limited by the large tail and stabilizers and the forward hump over the canopy that you're better off relying on your nose mounted .50 cals to do the killing. However, if you have a gunner with you and you get into a dogfight, the top gunner is useful and can be a major nuisance to any fighter trying to engage.
Ack-Ack
