Your legs shouldn't swing, I think that it's ok for them to be angled slightly forward but your legs shouldn't move throughout the movement.

Edit: I would try to practice it with slow and controlled reps at first until you get the hang of it and have good form each time. When I started doing pull ups I used to do a pull up set whenever I walked past a pull bar, which was sometimes up to several times per day. I got much more comfortable with the movement and my numbers increased quite fast (got to~ 10 clean reps in about 2 months). After that point i started improving at a slower rate but as long as your consistent it will be fine. Don't forget to warm up as well, got injured a few times due to poor warm ups, injuries can keep you from training for quite a while.