Watch the Intervals 3 online guitar lesson by Matthieu Brandt from Jump Blues
An open way of playing intervals as an accompaniment is by using sixths.
The mixolydian scale is harmonized by adding a second note that is a sixth higher then the original note.
The Bb mixolydian scale has these notes: Bb C D Eb F G Ab Bb
When you add a sixth, you get these intervals: Bb-G, C-Ab, D-Bb, Eb-C, F-D, G-Eb & Ab-F.
Hey, you'll never remember this if you're life depended on it.
Look at these examples to help you out.
Focus your riffs on these positions and vary them to your liking. Always keep your eye on the tonic and move with the chords!