You should definitely look at some professional shots in the poses you're trying to hit, and compare yourself and your positioning to them. I noticed a few things....
On the ab shot at the bottom, get your elbows up way higher and closer in. Your upper arms should be kinda right by your head, elbows pointed up, and slightly forward I think.
The back double bicep pose, you shouldn't be squeezing your back tight like that. You want to flare your lats, make your back look wider. Elbows a little higher on this one too.
your side bicep shot, open up your torso more toward the camera. twist at the waist. This one's a little harder to explain in writing, but basically you're making yourself look small by having your body turned the way it is. Get your back arm up as well.