Isometric series progressive Calisthenics. Bar holds

In order to do sets of pull-ups you need to be able to hold on to the bar. If you can’t hold
On the the bar, your central nervous system will let your body know and you will compensate by using muscles that are not ready. This will lead to poor form and not being able to progress.

Grab the bar with packed shoulders and hold on. Sets of 30 seconds are good, up to a minute is better. This will build grip strength and allow you to do more reps. If you can’t hold on to the bar, you can’t do pull-ups.