I am by no means a form expert, but with the help of TFOX (and others) I've done quite a bit of improving over the last year or so.

I snapped this picture with my self timer just a few minutes ago for reference. Greg gave you a lot of good information to think about and work on. I didn't notice it mentioned, but it looks to me as if your elbow is locked. If it is, try unlocking it. This may help you bring that shoulder down some.