Have a good stage presence
Psychologists say that it takes about three seconds for someone to decide whether or not they like you. So even the two seconds it takes you to walk onto the stage are important. Confidence is the name of the game here. You need to emanate confidence so that the audience wants to hear and believe what you are about to say to them. This only comes with time and practice. Whatever your craft, practice in front of an audience as often as you possibly can. The initial jitters will subside and you will soon learn how to command a crowd without even thinking about it.
Know what you're going to do beforehand
With any sort of performance, whether it be stand-up, music, or even just a short speech, you need to prepare and overprepare. Know exactly what you're going to say and do beforehand and have it down front to back. It can be fun to ad-lib, but that's something that only should be attempted once you have plenty of experience in front of a crowd.
If in the first few seconds of your performance you hesitate or look nervous, you will start to lose people immediately. It can also be easy to underestimate how nervous you will be once you finally get up there.
Preparing beforehand not only improves your chances of success, but also minimizes total disaster.
