Practice a 12-bar blues progression. In the key of C, the chords for a 12-bar blues are C major, F major and G major. The twelve bars (music measures) for this progression are divided into four bars of C, two bars of F, two more bars of C, one bar of G, one bar of F, and two bars of C. Learn this progression in the key of C to help you develop a feel for the blues rhythm.
Learn the blues scale. As with the chord progression, begin by learning it in the key of C. Once you learn the scale in one position on your guitar, move it to other positions. All scales can be played in different locations on the guitar. The more positions you practice with, the better you'll be able to play the notes. The blues scale is a major scale with the third, fifth and seventh notes flattened. For a C blues scale, the notes are C-D-E flat-F-G flat-A-B flat. These notes, played over a 12-bar blue progression, make up the blues sound.
Record several rounds of the 12-bar blues progression in the key of C. Play back the progression while you improvise blues licks using the C blues scale in. The flatted notes are the "blue" notes: they define the blues sound, so use them often. A blues lick is a grouping of musical notes tied together to create an entire phrase.
Add string bends to the blues licks. To bend a string, play a note on your guitar and push the string up or pull it down with your finger, causing the string to bend. This will change the pitch of the original note. Blues solos often start with string bends, and musical phrases often end with them. Incorporate shorter, smaller bends throughout the lick, as you see fit (blues music is heavily improvisational). Bending techniques can also save wrong notes by changing the tone of the string until the note comes into tune.
Incorporate vibrato and slides to bring more texture and emotion into your blues playing. To employ vibrato, gently rock your finger against the string when you play a note. This will give the note a vibrating, wobbling effect. To use a slide, start one or two frets below the note you want to play and drag your finger up to the note you want to play. You can also use a reverse slide, moving your finger away from the note after you play it. Slides, combined with vibrato and string bending, will make you sound as if you've been playing the blues your whole life.