Here's some of the advice I've received so far:
1) Learn blues licks in as many different keys as possible.
Ok, this first bit of advice sounds do-able (I think). I mean, there are loads of sources for blues licks and I've already got quite a few floating around in my head.
2) Learn as many blues rhythm patterns as you, including chord substitutions.
Ah, now we begin to hit choppy water. I'm not entirely sure what a chord substitution is. I'm rather hoping it allows one, when one is playing and is a little unsure of which chord comes next, to wave one's hands and distract the audience for enough time that the chord is not missed. But I have a feeling it's a little more complicated than this...
3) Learn plenty of licks to play over turnarounds.
The turnaround, from what I remember, is the end of the rhythm pattern when the tune 'turns around' back to the starting chords. This means that any licks you play have to fit across the chords in the turnaround. I think.
What all of this shows is that I have a lot to learn. Consequently, I've not got time to fanny around here typing; I need to learn me some blues rhythms...