Here is a quick run-down of my 2 favorite drills for resolving shoulder pain with two styles of pull-ups (traditional kipping and the butterfly).
These videos aren't "how to pull-up videos"; these videos will instead help resolve common faults. The cool thing is, these techniques can help if you are just starting to string a few pull-ups together or you have been on the pull-up bar for awhile and need to tighten something up.
Grab a fluffy cloud or a band, and get to work!! (Video)