A book I found really handy is Digital Texturing & Painting by Owen Demers.
While somewhat Maya-centric, the book does contain a lot of basic principles of texturing, including uses of procedural, painted, and photographic textures.
I found his suggestions for creating aging and dirtying up stuff in Photoshop (applicable in other apps) really useful.
He even shows you how to make a really nice texture out of Sculpey, a sponge and a quick paint job!
The book covers enough of the concept that you should be able to apply any of the techniques