First off, try a narrower grip.
For the negatives, 1) get your descent under control -- don't swing around, 2) slow them down, and 3) you have to take them all the way to the bottom. For 3, bend your legs or find a higher place to chin so you can do this. Chins are won at the bottom and you're leaving this out by relaxing early. Same thing goes for your chin -- don't start out leaning on the floor.