At the risk of giving away my trade secrets:
If you want to attack a bomber, climb until you are directly above it with about 5k of alt (if bomber is above 25k, just go home and grab a 262). Fly out ahead of the bomber (a short distance only, practise until you get this right) then chop your throttle and stay level until you are at about the same speed as the bomber. Then dive down, as close to vertical as possible, and chop the bomber in half, firing when at about 1k range and holding the trigger down until he is dead. The best spots to aim for are the pilot, the wingtip and the empennage just forward of the tail.
Gunners find this attack impossible to defend against and it is very easy to shoot at the planform of a bomber. Check my stats (under BLUEmako until tour 25) if you want to see how effective this attack is. The only time I die to bombers these days is when I get impatient and make a stupid dead 6 attack.