This article is from the Pool & Billiards FAQ, by Bob Jewett with numerous contributions by others.
You will probably receive all sorts of contradictory advice on this
one. The only real requirement is that you hit the ball low. If the
object ball is far away, you will also need to hit the ball hard to
keep back spin (also known as draw or screw) on the cue ball, as the
cloth rubs the spin off. Some things to keep in mind: You must chalk
your tip well; most players don't. A shorter bridge (hand to cue ball
spacing) will let you hit where you want more accurately. If your
elbow is pumping up and down, hitting the intended spot on the cue ball
is more of a challenge. Do you jump up at the end of the shot? Do you
follow through so the tip ends at least a ball diameter or two beyond
the original position of the cue ball, or do you jerk abruptly to a
stop at the instant of contact?