You want to get off to a good start as a blues guitar player, you will need five notes. Well, five notes in any key. The five notes you will need is a scale called the minor pentatonic. If you are playing in the key of E the notes you are going to be using are E G A B D.
The minor pentatonic scale and the changing relationships between those five notes will enable you to give your guitar playing the distinctive blues flavor. Get to know this scale by experimenting with simple tunes. You can make them up for yourself and play them up and down the guitar neck.
As you spend some time playing your own tunes you can listen to CDs of the great blues guitarists. Get familiar with how you are using the five notes of the minor pentatonic scale and see how the guitarists of the twenties, thirties, forties, fifties and sixties used them. See how those old blues guitar players played inside the scale and how they ventured outside it to add some spice to the blues. Listen to how they used slides, hammer-ons and pull-offs as well as up and down picking.
If you like the licks you are hearing in the work of the great blues guitarists, teach them to yourself. You need to be careful here. Your aim is not to duplicate note-for-note the licks of the greats, but you need to tap into the mood of their playing and see how it connects with your mood. Don’t be afraid to leave some empty spaces. You don’t have to fill your blues solos with notes.
Next, you can start getting into mixing the major pentatonic scale with the minor pentatonic. You will find that blues guitar players of the past did that to great effect. So, still playing in the key of E, but now mixing the minor and major pentatonic, you get the notes E F# G G# A B C# D. An important element of blues music is the flattened fifth note. It can be overused, so just look at it as another tool to help you learn to speak blues. So with the flattened fifth added, your notes are E F# G G# A Bb B C# D.
Now you have a bunch of notes that, played one after the other, will sound pretty ordinary. Go back and start experimenting with those notes. Make up some more tunes. Listen again to the big-time blues guitar players. Learn which notes are your bread and butter and which of these notes are to be used a little more sparingly.
If you want a little help to start you off, try using licks in the major pentatonic scale over the I and V chords. You might notice your minor notes go well with your IV chord.