In rock, jazz, and blues, improvisation plays a great role for any guitarist. In fact, being a good improviser is much more important than being a good technician. It’s much more important to create honest, credible, and inspired music through improvisation than it is to play with technical accuracy and perfection.
The best musicians in the world are the best improvisers, but they are not necessarily the best practitioners of the instrument. About the only thing that competes with the ability to improvise a good solo is the ability to write a song.
You’re going to take a collection of notes and turn it into music. To do this, use the 5th-position pentatonic scale. This is a slow, gutbucket blues shuffle in A. Don’t forget to swing those eighth notes and remember the blues credo: You don’t have to feel bad to play the blues … but it helps.
Improvising is, at the same time, one of the easiest things to do (just find your notes and go) and one of the hardest (try to make up a meaningful melody on the spot). The more note choices you have, the more vocabulary you’ll be able to pull from to express your message.
The pentatonic scale is a great way to start making music immediately, but plenty of other scales exist to help you in your music making. And you still have to listen to other guitarists for ideas.
Go outside any scale you use to get unusual notes, and learn passages of classic solos on recordings to see what makes them tick. Above all, you must develop you own sense of phrasing and your own voice.