Have been trying to get hold of the Guitar Compendium, but it seems to be out of print. I would greatly appreciate any suggestions for alternatives
The major and minor scales. Learn em, use em, love em

Practice with backing tracks on youtube. You can read any book you want but the only way you'll learn is by jumping in and just doing it.
And no, Guitar Hero will not help. Even on expert. Really.
Guitar Soloing and Advanced Guitar Soloing, by Gilbert and Marlis, are a good comprehensive intro to the subject.
how to improvise--hal crook
the advancing guitarist- mick goodrick (less improv, more foundational musicanship stuff)
the guitarist's guide to composing and improvising--joe damian
all the best.
(insert self-aggrandizing quote here)
Thanks for all the suggestions guys, Guitar Soloing and Advanced Guitar Soloing by Gilbert and Marlis is a great read, thanks for the heads up.
If you ever see the Guitar Compendium by Garry Hagberg really do check it out