Pull up

This is the most detailed form video I've seen, which I found from a reddit thread during rotator cuff research.

My biggest takeaway is do not passively dead hang at the bottom. This creates a bunch of shoulder instability and risk for injury.

Prerequisites

1. Strengthen your abdominal muscles
2. Strengthen your deadlift. Is this really necessary?
3. Strengthen your scapula
4. Lower body fat (it’s more difficult to pull excess body weight)

Positioning

1. Slightly wider than shoulder grip hand positioning, so that your elbows are in front. This helps engage your lats.
2. Grip deep into your palm (avoid a finger hook grip). Focus on squeezing your ring and pinkie fingers, since they're the weakest.
3. Plug energy leaks (Tighten your core, glutes, quads and keep your legs straight out and down in front of your body)

The Pull

1. Look up towards where you’re pulling
2. Squeeze the bar (squeeze with your pinky and ring fingers, the rest of your hand will follow)
3. Reach for the bar with your chest. This encourages thoracic extension which will make it safer for your shoulder. When your back is kyphotic, your scapula can't move properly over your bent ribcage.
4. Dead hang stability. Tighten your shoulders and scapula at the bottom of your pull and throughout. Create space between your traps and ears, but still allow your scapula to rotate outwards and upwards.