Great advice, thanks! I will work on this.
Originally Posted by BevelDevil
You're letting go of the throat too soon.
Use your left hand to drop the rackethead below the ball and only let go once you start with the forward swing. Compare with this vid:
The link jumps to the relevant section, but you should watch the whole video. (You can also find a 2-part series by this same guy, which is good.) Make sure you understand the "power position" concept.
On the forward swing, let your shoulders pull your arm and racket forward.
It also helps to straighten your arm earlier in the swing, before you let go. You'll get a more consistent and powerful swing pretty quickly that way.