A lot of times, the problem is simply one of not quite having something together that you thought was together--you should be as comfortable playing your leads as you are playing rhythm--this isn't necessarily hard--simply work out a few simple leads,(with blues, you are lucky, because you can play the same solo for damn near any song) and play them til they are second nature--Thing to remember: when you practice, play the solos all the way thru--too many times, people get into the habit of play up to to a certain point, then stopping--they end up knowing part of the solo really well, and part of it OK and little bits of it not at all--guess where they "lock up" in a performance situation--