Here's a couple suggestions. I sure wish I had a video of this because it's much easier to see than to explain.
First, when you have your feet behind your knees, you should try to keep them as flat as possible so you will have something to push with. Also, you could try widening your feet.
The arching.... what I try to do when I arch is do a backbend on the bench. Try and put your crotch on the bench. I know this won't happen, but that is what the goal is. Also, you can use the uprights on the bench to push your shoulders more towards your butt to create more of an arch. Once you are in an arched position and have the bar, squeeze you shoulder blades together as much as possible. That grip you have looks a little close... were you trying to do close grip that day? When you hear people tell you to keep your elbows in, this doesn't necessarily mean to move your hands in. I think Spatts has a video posted that shows the elbows thing.
Don't despair. These things take time to learn. The first time I ever tried them, they didn't work for me. Keep practicing and it will pay off in the end.