I came across this site in one of the forums, and it is an addictive read. The level of attention to detail is phenomenal, and if I could work on a car (and blog!) half as good as this guy, I’d be a happy man.
The single best piece of advice that had me chuckling for several moments:
it can help if your assistant is smaller than you and has a peaceful nature, that way you can b*****k him if the job starts to go wrong without fear of having your nose broken.
Seriously, there are some very good explanations of how gearboxes and engines work in particular, and techniques and tips galore.