I have a 2 door, but here is how I put mine on. I lay the top flap on and loosely attach the straps, then tuck the corners into the body. Then I reach under and wrap the bottom section around the top and push it upward. Then I grab the leading edge from the top so that I can start the zipper.
If you have a 4 door, make sure you have it folded correctly from the start. I see many 4 doors with the top folder so that the frame arms are on the same angle as the sport cage. Those arms should lie flat on the tub.
If you're not folding the top correctly, this video will show how. It's one of the best I've seen for expalining exactly how to do it.