@pablob I would recommend doing horizontal pulls such as bodyweight rows first, just as the RR in the sidebar says. Why? Well, first off, it trains your grip strength. 2) it allows you to use core tension so when you eventually do the pullup, you do not swing. 3) It helps raise body awareness and positioning since you have to keep core tension.
From there, you could try chin up and pullup negatives. If you have trouble holding the top, don't do this, and maybe try an isometric hold at the top with over or underhand grip because your biceps may need to be built more.
Got the isometric? Try negatives again. Are you swinging? Find a plyo box or large, stable base to get into position, and if the pullup station has vertical support bars close enough, hook your toe around it and slowly bring your legs back to center using your core muscles while in the lockoff you practiced.
Is your core not doing its work to stabilize bringing your legs back together? Supplement with a few core exercises. I like dead bugs or other functional core work.
Okay. Now. Looks like we can go back to negatives for the third time. Jump up or use the base, stabilize, and slowly lower. Keep videos or use a mirror for form check as well as progression.
Alongside negatives, you may also practice scapular pulls. The lowest part of the pullup may be the hardest because you are using the scapulae to pull, but they're not exactly the biggest muscles.
From there, you can try chin ups or pullups. If you can do 1 by now, try not to get super stoked an immediately move onto them and continue your progressions if you want to do more of them. You can even do your pullups and then negatives in the same set if you get too tired to finish the total reps you wanted.
On a few side notes, I do not prefer resistance bands. They have too much variable resistance and can slip and cause injury. Then comes assisted pullup machines. They don't put you in a similar enough position by pushing from the knees since now you don't need core tension. HOWEVER, they still help build strength if used correctly. Use them how you want, but be mindful, especially of your form.
Last but not least, if you swing when doing the pullup, keep your toes pointed and in front of you because legs crossed behind arches instead of hollows the body. Use abdominal muscles to keep feet in front to avoid kipping, which may equal swinging.
All the above is just how I have gone about showing others or climbing buddies how to get to a pullup. It is one of many ways you can progress. Thanks for posting here. We love this sort of stuff, and it may be what a bunch of other people wanted to ask.
TLDR;
Start with horizotal pulls such as rows (RR in sidebar), then isometric lockoffs, core, negatives, and scapular pulls. "Debug" your problem areas, and good luck!!!
