1. If you can't finish the sentence "the reason for my presentation is..." then don't bother doing the presentation.
2. Make it shorter. It's like packing for a trip. Pack like you normally would, then reduce it by half. Likewise, prepare your presentation like you normally would, then cut out half of it.
3. Don't read your slides. Instead, tell a story. Your slides will help us follow along. If there is something REALLY important for us to know. Slack us the details afterward.
4. If you find yourself singing (or doing an equivalent behavior), you've done something wrong.
5. Be present. Don't use someone else's presentation template. Make something yourself and make it your own. You are presenting for a reason. We want to hear from you. So let that alone boost your confidence. We are here to see your energy and get a feel for what you have to offer. Show us.
Another tip: unless you are swamped in presentations, never refuse a chance to present. You have something to share with us—teach us. We need what you have to give. Plus, if you're into learning stuff, there's no better way to learn something and become an expert on it than to prepare a well-thought-out presentation and teach a group of people about it.