| I like to practice chromatic scales, one finger per fret.
That means "index, middle, ring, pinkie" on the bottom string (e on a 4 string) and the same thing one fret lower on the next string, all the way up the bass and back down. If this doesn't make sense, I'd be happy to try and explain it more clearly.
p.s. I always do this kind of workout with a metronome, preferably with it clicking on as few beats as possible.
p.p.s. this is also a great excersise to try strict alternation. | 
