The voice cracking, red face etc are just physical symptoms, you need to get your body more relaxed. It's a vicious circle - you are scared, your voice cracks, then you feel even more scared, then your face goes red etc.etc. It's just physical symptoms though.
Take deep breaths before you go on, don't be afraid to take a few moments beforehand to calm yourself down. You don't have to be chatting and laughing with people who have nothing to do but sit and watch. One of the best and most experienced presenters I know goes and fiddles with the projector for about 15 minutes before presenting, he won't talk to anyone - once he's off stage he's fine.
Don't think about the audience - think about what you are talking about. Concentrate on getting your message across.
Practice your talk, with the clothes you're going to wear, and the shoes. Make it feel as familiar as possible. Practice in front of your DH/DC/friends if you can - do everything to make it less unusual.
When you are up there, try and look some of them in the eye. It reminds you you are talking to individuals, not a homogenous mass. If anyone yawns/falls asleep/rolls eyes, remember that is about THEM not YOU. Some people just can't concentrate on people speaking, while for others it's the best way for them to take in information.
They are not all sitting there thinking about you nude, they are thinking about what you are saying, or how nice it is to have a sit down, or what they had for tea.
Good luck!! When is it?