Watch the Blues Walking Bass online guitar lesson by Mimi Fox from Flying Solo
Though I played through the blues in two keys/two areas of the neck here, the essence of what I was doing is really the same. Use the two lowest strings on the guitar to create your bass lines (in general this is the best bass sound... but you can also sneak in a little bit of the 4th, and even sometimes the 3rd string if you don't over-use them). It's critical to learn your arpeggios on your lower strings and be able to play them in any sequence. Please see my book: "Arpeggio Studies on Jazz Standards" for help with this.