I have worked on a few lenses/ shutters in various sizes. I never worrried too much as well either. Just simple unscrewing, cleaning, and rescrewing it back. I just worked on two a few days ago. But I never worked on any that were too complex. I have done small range finders, TLRs, primes, and zooms.

Its not too hard, just organize and keep track of parts and use common sense and/or guides.