One word: Transcribe. Nothing will boost your harmonic vocabulary and chops like transcribing a good solo. Although scale patterns and stock licks are a good place to start, improvising is about translating the ideas you have in your head to your instrument. Transcribing will help train your ear, so when hear a lick in your head, you can instantly play it in an improvisatory environment. Start off small. The Miles Davis "Kind of Blue" album is a good place to start. Actually, any Miles Davis recording would be good to transcribe from (except maybe some of recordings in the 80s. "Time After Time" anyone?). Wes Montgomery and Jim Hall are definitely good guitarists to "borrow" from.
On the rockier/fusion-ier side of things, check out Scott Henderson, Pat Metheny, John Scofield, Mike Stern, Frank Gambale, and Allan Holdsworth.
To help you out with the transcribing process, I recommend Transcribe! by seventh string (
www.seventhstring.com). With this software you can slow down, transpose, and loop phrases. You can download a free demo.
I hope this helps!