I have to try and come up with a bass line for a blues piece I am writing. The problem is my bassist doesn't know how to come up with the simplest of bass lines. So for this blues piece I am looking for a little advice on what the theory is between a 12 bar blues line for a bass comprises of. It seems the bass uses very few chords so I am at a bit of loss. Any guidance?
heres a pretty funny one.. it sounds good, too.

D -----4-5-4------
A -4-7 ------7-4--
E 5-----------------

thats in A, the first note is the root of the scale.
I would do a line, say, in A, starting with a the root note, then hitting two frets above it on the same string. transfer that riff for the D and E parts, and there you go.
If it's like a blues/rock shuffle then the most common bassline is probably this:


Transpose that for the IV and V chord changes.

Relly all you need to know is the pentatonic scale and just noodle around together until it sounds good.
one i like to use in E is
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