A crossover dribble is a dribble that starts from one hand, bounces off the ground and goes to the other side. When preformed quickly, these can be extremely effective. They can be used to keep the defense from stealing the ball or to get past the defense. You want all of your dribbling to be below your waist and the lower they go the faster and the better. Just make sure that it is not out of control. The further away the hands are from each other the harder it is.
Look at the pictures for help. This is how you execute a nice crossover move in a game. Start out with the ball, dribbling with your left hand. Now quickly take a wide step to your left, leaning and head faking to the left as well. If your man doesn't react to this then drive by him on the left side. But if he goes for the fake then the next step is to cross him over and go right. You must totally change direction and bring the ball way over to your right so that he can't knock the ball away as you are going by him. Push off from your left foot and speed towards the basket. If you do not run full speed then the defender will recover.
This is similar to the crossover that Allen Iverson of the 76er's does except that he does not drive so soon, he crosses him over again and drives with the ball in his left hand.
Like all moves don't do it too often or else the defense will know it is coming. What you could do is do it maybe like two-three times then the next time you fake left, hesitate, and then actually go left.