Math's tips are ok but the techniques he describes require you to get well inside the AAA envelope of your targets. The best approach is to:
1) Download and install a gunsight that has markings for rockets and bombs (I use a variation of mino's sight, attached). The top tick marks are for rockets, the bottom for bombs. They are accurate for a 45 degree dive angle.
2) Approach targets at 10k alt above ground.
3) Go into a 45 degree dive with the throttle closed.
4) Line up with your target using the bombing marks on the sight then stabilise for a second or two before releasing bombs.
Note when you drop bombs or rockets your plane should be wings level, not yawing or banking.
5) Pull out and barrel roll to avoid any ack.
6) Practice, practice, practice.
By executing a 45 degree diving attack you can get good accuracy and only enter the upper fringes of the ack envelope at your target. With practice you can line up and drop from above the ack envelope, keeping you a lot safer than vertical dives would.
This technique is learnt and all it requires is practice, not mysticism...