The way I do the over/under wrap is something like this:
1 - Extend your arm and put your palm facing away from your face. Put one of the cable ends between your thumb and index with the plug facing away from your face and the cable going towards you. Do this with your left hand if right handed, right if left handed.
2 - Imagine you're holding a ping pong racquet in the hand pulling the cable back.
3 - Make a normal out loop. Do this with the motion you'd do when lobbing the ping pong ball from in front of your body. Try making the loops the same size.
4 - Now, for the under loop. Pull some more cable back. Now imagine doing a forehand stroke with the racquet. If you're right handed, this means extending your arm to the right to hit the ball.
Do the ball hitting motion, making sure your arm goes under the cable coming out of the opposite hand like shown in the pic:
Put the cable between your thumb and index of the hand holding the cable and join the loops. The remaining cable should come out between the 1st and 2nd loop.
5 - Repeat alternating between over and under loop.
