Do it lots, and, if it goes wrong, get past it and try again.

I had a "composure problem" for many years. Then I got asked to emcee at a folk club, and failed to say "No", and over time gradually got more comfortable in front of people, although the nerves never totally went away. As Celtic Soul said, nervousness is close to excitement. You should be a little keyed up, in a positive rather than negative way. Passion is good. If you get totally blasé about performing, your performance will get mediocre.

Do a lot of visualizing of your set going well, with great audience reaction. Play the whole set in your head at least once beforehand, maybe the afternoon of the gig.

Allow yourself five minutes of abject terror a few minutes before you go on stage. Then you'll have gotten that out of the way already.

Remember that, for the most part, the audience are on your side. They want to be entertained, so they want you to do well. If an audience is hostile, you've accepted the wrong kind of gig.

It's also possible to construct a "stage persona", much like yourself but more cool and confident, and portray that character onstage. I'm a tad klutzy myself, and try to use that in an amusing way in my stage persona. Also, if you portray a character for a long time, you take on some of the characteristics of the role in real life. But your stage persona shouldn't be too much different from your real self, otherwise you get caught up in acting rather than making music.