I am playing guitar approximately ten years but I know only basic harmony and rhythm guitar.
I want to develop theoretical and practical harmony. What can I do for this?
Guitarists tend to learn chord shapes, and to learn rules about what chord can come next.
But chords aren't stand-alone entities, they're a collection of notes which, seperately or in combination, create tensions which can be resolved by moving to other notes. You know that G7 wants to go to C. (Otherwise why would it be a pleasant surprise when it goes to Am instead?) You need to get inside that G7 chord, feel the G pulling towards C (particularly if it's in the bass), the F pulling towards E, the B pulling towards C. And, hey - all those pulls are satisfied by going to a C chord! Most of them are satisfied by going to Am. Some of them by going to A major or Ab. None of them by going to F#. So that's why G7 - C is the "standard" move, G7 - Aminor or G7 - Ab sound interesting but possible, and G7 - F# sounds way-out.
I could show you this very easily. I suggest you sit down with someone who can. Otherwise you'll try to do it all by numbers and rules, and get bogged down in the Circle of 5ths diagram.