Watch the The Blues Box online guitar lesson by Rob Garland from The Guitarist's Pentathlon
Forcing yourself to play in one small area of the neck on one set of strings is a great way to focus on phrasing. I suggest staying inside he box, leaving space and building a theme. Be aware of the location and sound of surrounding notes for bending, such as the b5th and the major 3rd. Also don't forget to experiment with dynamics, playing with your fingers vs digging in hard with the pick, be as expressive as you can, it's is the blues after all.