Pentatonic major/minor is a good basis, but extra stuff to add variety also works - the "nuts in the brownie" syndrome, if you like. It's a good idea to get a jam track tape/CD to play along to, then you can find what works and what doesn't - training your "pure instinct", in other words. But pentatonic is the "bread-and-butter" of blues playing.

Pentatonic A minor/C major scale is { A, C, D, E, G, A }. Blues A minor scale adds D#, often used as a "passing note" between D and E. Blues C major scale adds F#. If you're playing in a major key you can use the D#/Eb as well to get the major/minor switching thing going that blues uses a lot of, and adding the F# to minor keys works pretty good as well (but don't overuse it). You can also add in lots of minor sevenths when playing in a major key (in C, get your Bb finger working!) - you don't often use major sevenths though, except as a passing note between Bb and C.

In other words, think pentatonic as a basis, but add in whatever you damn well feel like! And if you ever drop a real bum note, just keep going in that direction and ppl will think it was intentional! :-) If you really can't think how to get out of it, convert it into a chromatic run up or down to somewhere safe and pentatonic - that always sounds good so long as you use it sparingly. Graham.