Merely taking something apart and reassembling is a rote process. What will help you the most is observing the function of the various parts, how they interact, and wear patterns. Written instructions will typically be much more accurate and thorough than videos, especially at sheldonbrown.com and parktool.com, and often will explain more of the why rather than just the how. Videos can be helpful in seeing the live process, but I would advise caution, as some do not use proper techniques or have outright errors.