One thing you might want to learn are the modes and how they work. The modes increase your musical skills a lot.

One good book is "A modern method for guitar" or a book serie that is.. It's not very new but it has almost everything and it doesn't teach you anything about any styles, just basic plain stuff.

For example Steve Vai and John Petrucci have played the book and now it throughout because they have gone the Berklee University that teaches the book for it's a musical university or something like that..