If you're still not convinced that you should be doing some sort of pull-up variation in your program, consider it as one of those biggest-bang-for-your-buck exercises. They essentially work everything above the belt, including:
Shoulder - Teres Major, Infraspinatus and Teres Minor
Long Head of the Triceps
Forearm/ grip strength
Core (External Obliques)
Let's talk about grip...
Although people usually refer to everything as a "pull-up," there is a different between a “pull-up” and a “chin-up” and that is the type of grip you take on the bar. Chin-ups (palms facing you variety), has been shown to work the biceps and the chest muscles a little bit more than the other hand positions. The wide grip pull-up activates your lats and your lower traps a little bit more. Chin-ups are known to be a little bit "easier" and would therefore be a great option for beginners. Honestly, unless you are training for something specific, it doesn’t matter. You will be getting strong regardless of which grip you are working with.
Here are two challenging progressions from those posted in Get Pull-Up Strong Part 1:
1) Band-Assisted Pull-up
This variation is great for teaching core engagement involved in stabilizing yourself during a pull-up; the more your core is engaged the less your body will swing when loaded in the band.
**The thicker the band = the more of your body weight that is supported = the easier the movement
PROGRESSION -- Add reps every week and eventually use a thinner band.
Loop band around pull-up bar (long “monster band” – band thickness can vary from 2 inch to ¼ inch)
Use box or step to help loop foot in band
Begin pull-ups –slow and controlled – engage core to limit swing
Be careful on dismount, stepping out of the band one foot at a time back on the box.
2) Negative (Eccentric) Pull-Ups
This is probably one of the BEST and most challenging ways to get closer to doing a real pull-up because it is the most similar variation.
At the end of the day, the best way to get better at pull-ups is to strengthen the muscles involved in the movement by doing pull-up-like-movements multiple times a week. Smart and consistent training is key.