This ExtremeTech article has a few Gmail Power tips, taken from their book called "Hacking Gmail". If you're the sort of person who can't learn about something like Gmail by screwing around with it in your browser for 10 minutes, then you might get some value out of the article and/or the book (and/or selling your computer and going into retail or something, but that's another story). Be aware though, it looks like this thing was written a long time ago - the screenshots still show Gmail at it's 1gb maximum, as well as in the days where you got 3-5 invites.
This proliferation of books covering simple subjects aimed at stupid people is a bit of a worry. What happened to the good old days of actually having to sit down and use your fucking brain for a while.