Watch the Lesson 15 online guitar lesson by David Hamburger from Fingerstyle Blues Handbook 1

If you use your index finger to play the melody notes in measure two, it's awkward to jump back up to the third string to play the melody notes in measure three with your index finger as well. Instead, try using your middle finger for those third string notes. You could even play the opening phrase with your middle and ring fingers. It's a tossup whether to do that or just start out using index and middle in measure one, and shift them both down for measures 3-4.