show/hide this revision's text 1 [made Community Wiki]

Assuming you already know undergraduate algebra (and maybe a little basic homological algebra already), the book Methods of Homological Algebra by Gelfand and Manin is a good source for the kinds of things in the first chapter or so of Kashiwara-Schapira, i.e. derived categories, derived functors. I can't remember how elementary its sheaf theory is, but a little background in sheaf theory wouldn't hurt either. Swan's book is probably a kinder starting point for sheaf theory then Bredon.