flexible scales (like mention in the other "how do you practice" post), play around them freely, trying to use as much of the range as possible, it's how I do 'em at least, and besides its fun.
There is a Jamie Aebersold book "Blues in All Keys" with CD which consists of 12 x 3-4 min backing tracks for each blues scale. Very useful as you can practice one at a time, and gradually play several in one session. Very useful IMHO
if you look in any jamey aebersold book there is a page of 10 daily practices
exercise 9 and 10 are blues scale exercises which build on the scale starting with the first 3 notes.