I usually find the time before I'm due to go on much worse these days - I'm fairly happy once I get up on my back legs. But I find my fingers seem to wander off somewhere in a world of their own, and never do as well as they did rehearsing. Maybe the answer to that is work, work, work?A couple of things that can help when performing: get a partner, especially one that's more experienced than you are (share the blame!); if you don't play an instrument, sing from a chair, but have it the wrong way round, so you're leaning your arms over the back - this keeps your diaphragm and all the other innards in a good singing position.
What I REALLY hate is practicing in front of other people - I'm quite happy just performing!
Steve