I do them all the time, and don't like any rep over five lol.
4 x 10 full range, I would consider very good.
To improve, do them every day, in small clusters, like the following:
1 pull up
(Rest)
2 pull ups
(Rest)
3 pull ups
(Rest)
1 pull up
(Rest)
2 pull ups
(Rest)
3 pull ups
(Rest)
That's 12 total reps
Aim to rest 5-10s between reps
You'll improve quickly.
Other tricks are: wrap hands "over" the bar, flex abs and ass, be slightly concave with legs forward a bit, not crossed behind. It limits sway, which helps.