@karebrown Hmm. Not sure which level of band you've used, but I would approach this like any "heavy weight" movement. You don't just start squatting 135#, right? You start at a low weight with higher reps, and linearly progressively work your way up. How to do that with pull-ups? For my example, let's consider green (thick), blue (medium), and red (thin) bands. Also, disclaimer, be careful with your shoulders, as they will also be heavily worked during this. You may want to take the following day COMPLETELY off of exercise to ensure at least 48 hours to repair your muscles.
Start by picking bands that allow you to do 8 strict pull-ups + 4 kipping pull-ups. Muscles tear most when you go to failure and then rest for 2-4 minutes between sets, so go to failure. Probably 3-5 sets to failure is more than enough, one time per week. Stick with the same bands that whole workout (you will do less reps each set as your muscles tear and fatigue). Then ensure you drink a protein shake before, during, or immediately after you finish to give your body amino acids to produce cells to repair your torn muscles. Let's say you are able to do this with a green band and a blue band.
The 2nd week, use a green band and a red band, and again, go to failure with strict + kipping (the kipping at the end of each set allows you to maximize muscle failure by adding some momentum).
The 3rd week, use just a green band, and expect to hit about 60% of the reps you did the 1st week (5 strict + 3 kipping). But then stick with that green band for another 2 weeks until your sets get back up to 12-16 reps.
On your 6th week, do ring rows instead, but same strategy of going to failure, resting, consuming enough protein.
On your 7th week, drop to a blue band only, but ensure you're doing 12-16 reps per set.
Depending on how quickly your muscles will develope, you may need to add an extra week here and there at the same resistance, but ensure you always increase your reps by at least 1 per set. The key is going to failure each set for several sets, and maximizing protein (amino acid) saturation in the body.
The importance of going to failure is that muscles only grow by getting torn and then your body sending new muscle cells to repair those tears. It's not good to go to failure during a metcon because there's little rest between sets, so your muscles never get a break and don't actually tear as much as if you rest for a few minutes then go at them again.
Many people think they are tearing and repairing muscle during exercise, when in fact they are not actually. Just because you are working a muscle and feeling a burn, does not mean the muscle is getting torn. Muscles tear from fatigue, which translates to doing sets to failure with rest in between. But then you need to REST and let your body repair the damage. If your muscles are constantly in a state of damage, they will never repair and you will not improve in strength.