how aren't you getting it? are u not reaching it, or unable to cross it up. So if your spinning to the left your gonna want to go left ski over the right, and grab your left ski with your right hand. If you spin to the left and put your right ski over your left and grab it with your left hand its an reverse mute, and viseversa for right side spinning.
A good way to practice grabs is to go into the half pipe, that way you can get so many jumps back to back with consitency. But if your having problems getting your hand to grab your ski... Then you should try to bring your legs up towards your hand, and not your hand reaching for the ski. Pretend when you go off the jump that your gonna do a cannon ball, and bring your knees up