Watch the Breakdown 3 online guitar lesson by Andy Aledort from Slow Blues Power
Starting with the E7 voicing on the top three strings, I use all upstrokes to strum this chord so that the higher strings in the chord will sound more prominently. On beat two, while strumming the chord, I alternate between the G# on the high E string and an open high E, providing a bit of melody to the improvisation. On beat three, I pick the top two strings individually but allow the notes to ring into each other.
Over the A7 chord in the next bar, I simply lower the notes on the top two strings one fret and sound C# and G simultaneously; as C# and G are both chord tones of A7 (A C# E G), they make clear reference to the chord and sound very effective. Looking closely at the intervals, C# is the sixth of E, but it is the major third of A, the chord that this riff is played over. The notes of A Mixolydian are A B C# D E F# G.
I alternate between the top two strings in order to make this figure sound interesting both melodically and rhythmically; the melody is provided by the descending notes on the high E while the C# remains constant. On beat three, I play another trill, this time between the open B string and C#, and end the bar with the same quick slide-down on the G string that was played on beat four of bar 1.