Uncle Dave as ever is spot on.

If I may add some personal experience... I'm in a Duo (keyboards / drums) that used to back a very good frontman. I was out of it for a while and in that time the frontman disappeared and a guitarist turned up. Ultimately I rejoined and the guitarist left so me and my friend found ourselevs having to go out without alone. We were very worried that we would not be able to contact the audience given that I'm half obscured by keyboards and he's equally half obscured by drums.

Fears unfounded. We've never had a problem. The two big points (as UD says) are ENJOY (and more to the point make it totally clear you are enjoying yourself) and TALK TO THE AUDIENCE. It doesnt actually matter what you say so long as it isn't insulting. Try to avoid gabbling; speak at half the speed that you want to speak at; everyone talks too fast at first. You have to avoid the "30 second silence whilst I cue up the next song" problem. You can lose an audience with even 5 seconds of silence.

Also, if you screw up (and you will) stop dead rather than dig deeper. Again some chat about "how it worked fine last night" or "I really must practice that one" (or my favourite) "where did I put the instructions" should cover the gaps.

Have fun - you gotta have fun!!!