To me, it looks like you need to work on waiting for your horse to come up to you. You look a lot like me in my first year of steady jumping lessons. Instead of bending at the hips slightly, you're letting your whole body go forward.
To strengthen your muscles, working in two-point for ten minutes each ride and alternating that with proper no-stirrup work will help greatly.
What helped me was to ride in an arena with mirrors. I know what I'm supposed to look like, but I didn't know how to make my body do it. By looking in a mirror, you can adjust your position and then try to remember how the correct position feels. This will be great for your two-point work.
Another thing that has helped me greatly is not worrying about getting into jump position when I jump. Just make sure you release, and your horse's takeoff will do the rest. You may find that you need to move out of the tack a little more later, but for just starting, just quietly sit and just think about your release.
I know you mentioned in another thread that your horse has started to run out sometimes. Jumping ahead can cause run-outs - the horse knows that he can get away with it because you are not in the position to correct him. Perhaps correcting your position will also help with that!
If you can, do some grid work. Get your horse moving out, and then focus on your riding. Since the striding is set up to be a "no-brainer," it should really help you get a feel for your horse's movement.