very easy, just have to know what your target is going after first
if its another plane, make sure the pilot is busy trying to bomb somethin, when you are at his tail he is either toast or you two are stuck in a long long dogfight which works well also (stops him killing your teammates)
if its a tank, then circle it and bomb away, takes some practice to learn how to bomb well
if its a soldier, just shoot him, bomb him, mow him, easy targets unless he gets in a good cover then ignore him and find another target
if its a AA gun, best option is to fly as high as you can and then swoop down on him, easy to target your bomb and he wont notice you untill its too late (busy watching the horizon), second best option is to fly below him, he cant shoot past 0° angle and most of the time its maybe 10° because of sand bags and other objects.
Playing against planes
As a soldier, run for cover first, second locate the nearest stationary machine gun, they are almost or even sometimes better at taking down airplanes
As a tank, take a sharp turn when you hear the airplane, screws up their bombing aim, press 2 to take control over the machine gun and shoot it like mad, they will either run away or just die
As aa gun, always target waaay ahead of the plane, watch the black smoke, thats where you are doing damage.