As guitarists, we tend to use the minor pentatonic scale or "blues box" way too much, especially as beginners. And c'mon people, let's stop disrespecting a great music style by playing the same thing over and over again - there's more to the blues than just 1, b3, 4, 5,
First, let's talk about the most basic of the blues style: the 12-bar (I-IV-V) blues progression. Usually someone will noodle with the I Minor Pentatonic
over that. One thing that often confused me is that the I chord is
usually played as a major chord, yet we play a minor scale over it. Isn't that
against the rules? Well, the modulation of the major and minor 3rd is the
foundation of that sound we call "blues". You should use the b7 tone instead
of the major 7 tone, because the b7 tone sounds more bluesy, and the b7 can be
found in both major (Mixolydian) and minor (Dorian, Aeolian, Locrian,
Phrygian) scales. So, you can sound a little more original by simply making
the chords minor and using a Mixolydian Pentatonic scale (1, 3, 4, 5, b7),
and still get the blues sound.
To expand your melodic approach even more, let's try using a scale that
isn't pentatonic. In my opinion, the two best modes to use over blues are
Mixolydian and Dorian. Why? They only differ in their third - Mixolydian
has a major third while Dorian has a minor third. So, we could use Mixolydian
when we're playing over minor chords and Dorian over major (remember, we want
to get that modulation of the 3rds going). Or you could just make an 8 tone
scale consisting of 1, 2, b3, 3, 4, 5, 6, b7; this would put the modulation
in the lead line. Then, you could also do that in the harmony (play a minor
7th chord and hammer-on/pull-off the major 3rd note).
To expand your harmonic approach, we can do chord substitutions, or add
color tones to the chords. A simple way to make the progression sound more
jazzy (better) would be to play something like I(13)-IV(9)-V(13). The Miles Davis tune, "All Blues" uses a I(7/min7)-II(m7)-bIII(maj7)-II(m7) progression (the "7/min7" means modulate
the chords 3rd from major to minor quickly, usually with hammer-ons/pull-offs).
The main thing that I want to get across is that the blues sound is
created by the dominant 7th tone, and by the third, modulating from major to
minor. This is an important realization for any blues or jazz player.
Editor's Note: For some soloing ideas regarding this minor 3rd/major 3rd duality in the blues, look at Lesson #230: Blues Soloing and Basic Harmony