An amusing pitch, the knuckleball seems to defy physics with the way it dances towards the plate. Ironically, it is the same laws of physics that make it do what it does. Without any rotational momentum, it doesn't create any stable airflow around it, causing it to move at the whim of the tiny air currents around it. The knuckleball is the hardest pitch to hit in baseball, but unfortunately, it's the hardest to throw... so let's get started.
The grip of the knuckleball is pretty simple. Put your thumb on the underside of the ball, and dig the nails of your remaining four fingers into the top seam. The knuckles of your top fingers should be bent away from the ball -- THE KNUCKLES DO NOT TOUCH THE BALL! To throw the knuckleball, toss it like a regular pitch -- as you release your fingers will kill the normal rotational momentum of the ball, making it incredibly susceptible to outside forces.
The problem with throwing the knuckleball is that in order for it to be successful, the ball has to turn no more than ½ to one full rotation during its journey to the plate. Any more than that, and you're just throwing a really bad change-up. But if you can manage to spin it that slowly, few people are going to be able to hit it.
A word on the knuckleball: It's not going to work. Tell yourself that now, accept it, and move on. Have fun with it as a novelty pitch. Casually throw one when your team is up by nine or ten runs. Do not depend on it as you would any other pitch. There are only two knuckleball pitchers in the major leagues today: Tim Wakefield and R.A. Dickey. There's a reason for that.
Another word on the knuckleball: If you have to ask if it knuckled, it didn't. Many times, if a pitcher is working on a new pitch (in the absence of a pitching coach), he'll rely on his catcher to tell him what happened. He'll ask "Did it break?" or "Did it sink?". And the catcher, usually just trying to be a nice guy, will reply, "A little." And maybe it did, as a beginning pitcher usually gains only a little break on his breaking pitches. But if you ask "Did it knuckle?", and he answers, "A little."... it didn't. If your catcher dropped the ball, dove to block it, or missed it entirely, you're on your way.