The strategic bombing campaigns of WWII, for the first time in history, brought war deep behind the lines to the general civilian population. Although the debate still rages over the ultimate success of strategic bombing, all other things being equal, it seems better to not have one's country bombed. Air combat is usually romanticized as fighter-versus-fighter dogfights; however, such fighting really does nothing to further the war aims. Offensive fighter operations must seek out those enemy elements capable of attacking friendly forces in the air, on the land, or on the sea. Defensive fighter operations are designed to block such enemy offensives. Only then do fighter-versus-fighter dogfights truly support the war effort. Consequently, fighter pilots must not only be proficient at dogfighting, but at intercepting enemy bombers as well.
One of the most important aspects of intercepting bombers occurs before ever taking off in a fighter: learning about the enemy. Target recognition is vital. To effectively engage a target, one must know that target's strengths and weaknesses. Where is the heaviest armor plating? Where are the largest defensive guns? Which guns overlap their fields of fire? Where is the bomber most vulnerable? Learn what each bomber (both friendly and enemy) looks like. Learn what armament it carries and how the armor is distributed. In short, know what you're going up against.
Once airborne, engaging bombers requires a different mindset than engaging other fighters. Against a fighter, the ultimate goal is to saddle up on the opponent's six o'clock and stay there. This tactic amounts to suicide against bomber formations. At first glance, attacking bombers from astern is attractive. You slowly approach a stable, predictable target and gun its brains out. Bombers, though, carry defensive guns and you present a similar stable, predictable target when closing from behind. The bomber's gunner has plenty of time to aim the weapon, shoot, refine his aim, and shoot again. Instead, it works best to make sweeping, high-speed passes from the bomber's front or flanks. This limits the time the fighter is exposed to enemy gunfire. Further, crossing between the bomber's weapon arcs means each gunner has to acquire the fighter, aim the weapon, and open fire, with no individual gunner having the opportunity to refine his shot.
Remember to shoot for critical areas. Aim for the engines or (in a head-on attack) the cockpit. Shooting off the wings, knocking out engines, or killing the pilot will ensure the bomber goes down. Killing the gunners may be satisfying (especially if they've scored hits on your fighter), but generally won't prevent the bomber from completing its attack.
Also, remember that WWII bombers are relatively under-powered at combat weights. You don't necessarily have to destroy the bomber; knocking out an engine or two will almost certainly render it incapable of reaching the target. This is the difference between a "kill" and a "mission kill." The bomber in question may very well make it home, but if you've kept it from hitting its target, you've succeeded. If the bomber has already dropped its payload, knocking out an engine or two may force it down before it can get home, resulting in one less aircraft and aircrew for the next attack.