Blues guitar can be tricky because, for a simple style of music, blues generates a lot of heated debate on how to listen to it, how to play it, and who is any good at it. There is even argument about the blues guitar scale. The starting point for playing blues is a scale containing “blue notes”. An example is the E minor pentatonic scale with a flattened fifth. Using the I IV V progression, the chords would be E A B.
There are many ways to approach blues guitar soloing, and one alternative to the minor pentatonic is the Mixolydian scale, which is almost the same as the major scale. One difference is that the root note of the Mixolydian is the fifth of the key you are working with, so in the key of E the scale starts at B. The other difference is the Myxolidian has a flattened seventh.
Here’s a video showing how to use the Mixolydian scale:
One of the problems with discussing blues guitar playing is that we start explaining things using theoretical terms, and this makes translating theory to playing music a little difficult. If getting your head around scales and modes does not seem like playing blues to you, then you should just learn some riffs and turnarounds, and the twelve bar blues progression. After a little while you will see where to use seventh chords, and where to flatten notes.
Here is a video lesson on turnarounds in the key of E:
This lesson should give you what you need to start imitating the playing you hear on blues guitar records. But do not try to be too exact, note-for-note renderings of other people’s solos will sharpen your ear, but they will not help you with improvising. The essence of learning to make up your own music is to start fooling around with what you are listening to, and adding your own variations.
Here is Justin Sandercoe on improvisation: