Here's a technique for aiming that I've come up with. It's pretty simple. Consider the fact that a common billiard ball is 2 1/4 inches in diameter.
That means that when the cue ball contacts the object ball, there is 2 1/4 inches from the center of one ball to the center of the other (that is, provided the cue ball is not larger than the other balls, as is sometimes the case on many bar tables, but I'm approximating here). Once you have determined the line of aim, simply shoot for a point along the line of aim that is about 1 inch behind the object ball.
There is no substitute for practice of course. That is the best way to develop a good eye for shooting. But if you are having trouble with your aim, it's a good method of double checking. And it can be very useful on snooker tables, where aim can be made even more difficult by the larger size of the table and the smaller size of the balls. Let me know what you think. I would like to hear any feedback people might have.