There's some really good advice in this thread. I'll join with others in saying that you should keep your breaks simple, and resist the urge to play at maximum speed and with maximum flash. A slow, simple part played confidently will always sound better than a fast, flashy part that is a little beyond your reach.

Also, I notice in one of SlickerBill's postings that he froze up when a singer surprised him by calling for a solo out of the blue. There are a lot of singers/frontpeople who like to do that, but they really should not. Instrumentalists should know when their breaks are coming up, so that they can be prepared to launch their solos, and also handle the transitions into and out of the solo (playing a well-constructed intro to the solo is half the battle). If you are playing with a singer who likes to call for solos on the spur of the moment, with no warning, you may want to suggest that he or she not do that in performance (they can still pretend that it's a spontaneous outburst, as long as the band members know better).

And yes, as so many have said, keep at it -- playing in front of audiences does get easier the more you do it.