How can I be a straight backstroker, not a crooked backstroker?

Well, there is a lot of things that you need to do. First like Justin said, you need to keep the same amount of power in both arms. Second, you need to rotate your shoulders to keep you stable. This also makes you go faster. Lastly, you need to keep your head looking up at the ceiling (or sky) and not let it wiggle around. When your head wiggles, you wiggle. Also you need to keep your stroke from going onto the water with a bent elbow directly behind your head. If you do this, your hips move from side to side, causing you to circle swim. This should help!