It kinda looks like you rush your motion. Try to relax and slow it down a little bit. May help on your racquet head speed.

It looked like you were miss-hitting alot. You were using a pretty extreme grip, so try to toss the ball a little further back. This will help you get more topspin on the ball, making your slices more consistant.

When slowing your motion down, it gives you time to load all your weight into your legs. Explode up into the ball.