Chin ups = upper body squat. Although you can do them everyday, if you start off trying to do that you'll overtrain and give up.
Every other day if you build up slowly, or 2 rest days if you ramp up your volume and blitz it.
Cues and form tips to get the maximum benefit -
- full range or fuck off, i.e. All the way down to straight arms, no catching the bottom with your biceps
- focus on pulling your elbows down to your waist and slightly behind you
- try to get your chest to touch the bar
- as you pull up, squeeze your shoulder blades together
- lower yourself as slowly as you can
- flex your biceps and back hard at the top of the movement and hold there for a count of one
- keep your legs still, no swinging them around
- one slow high quality rep is better than 10 half reps where you cheat and wriggle your way up