Dimebag Darrell talks harmonics: "How to get 'em, where you can find 'em and what you can do with 'em."
Learn how you can use harmonic arpeggios to build interesting lines when using a 7b9 diminished scale in your soloing ideas.
Dress up your riff ideas with murky, monstrous-sounding, aggressively attacked chord figures and patterns.
If you don't happen to have synesthesia, that doesn't mean you can't use its general concept as a compositional tool.
An exercise that uses all the inversions of any chords you're learning, while playing them in a common chord progression at the same time.