Watch the Bubble Parts - Part 3 online guitar lesson by Jeff Scheetz from Blues Jam Survival Guide
Find the root note and then vamp on that. You can play the root and the fifth during bubble parts. Because unlike our guide tones (the 3rd and flat 7th) which define the chord - we want our bubble parts to be a bit more nebulous and less defined. That way if we get lost or are not really sure of the chords it can fit anywhere - and if we are adding a bubble part to an existing chord groove, the part doesn't get in the way harmonically.