After you have picked up the ball you need to set your feet and make sure they are even. Also square your body up to the basket to insure a good base for shooting the ball.
To go along with your shooting hand put your supporting (opposite) hand on the side of the ball for support. That is to help keep the ball from falling off your hand.
While in the air at the high-point of your jump release the ball from your hand. Be sure to flick your wrist to get the spin on the ball that you want.