One of my favorite photography books of all time is a remarkably simple book called On Being A Photographer.
It is by David Hurn and Bill Jay and has surprisingly few photographs. It is about the thinking processes involved in making good photographs. They do not talk about gear. It applies to any kind of photography, film based or digital. It is about thinking and seeing and thus is timeless. Anyone who is serious about photography should get a copy of On Being A Photographer.