There are many variables to consider to accurately drop "dumb" bombs (bombs that are not guided on the way down.) The most important variables are aircraft ground speed, heading, and altitude, assuming straight and level flight. If the bomb is released in a turn or during a climb or dive, other variables become very important. Wind direction and velocity is also quite important if the bomb is released at any significant altitude.
Try this experiment at home. Put a cup on the floor. From chest height, drop a coin into the cup. You will release the coin when it is directly over the cup. Now from chest height drop the same coin into the cup while walking past the cup. You will find you must release the coin earlier, BEFORE the coin reaches the cup so that as it travels forward, it drops into the cup instead of beyond the cup. The problem for the pilot is that his aircraft is traveling MUCH faster and the bomb is dropped from a much higher altitude.
Aircraft since WW2 have had computers that try to take into account all the variables. None worked very well because there are variables (like wind) that are impossible to measure or predict. That's why during WW2 it took many dozens of bombers each dropping several dozens of bombs to destroy one factory. The great majority of the bombs simply missed the target.
That's why "smart" (guided) bombs were developed. They steer themselves to the target which automatically compensates for any variables. There are many different types of guidance systems, with each having an advantage over the other, but none that provide the best solution for all targets.
The CEP (Circular Error Probable, which is the size of the circle within which half the bombs will hit) for a guided JDAM bomb is less than 10 meters. The CEP for unguided conical bombs released at 10,000 ft is just over 225 meters.
At the peak of the Vietnam war, the USAF was achieving a CEP with dumb bombs of about 135 meters with a direct hit percent of 5%. That is VERY good for dumb bombs. The CEP dropped to about 7 meters during Desert Storm with a 48% direct hit percentage.
Hope this helped.