No matter the situation, you need to arrive early and be ready to start at the appointed time. Once at the helm, you may decide to wait a few minutes if some of the principals are running late, but you should never, ever, leave your audience waiting on you. Even if the abandoned attendees don't give up on you and leave, they will be taking mental notes that may hurt your credibility. If you are traveling to a different site, give yourself about double the travel time you think you'll need to allow for delays. So if you have a job interview and it should take you an hour to drive from your location, schedule two hours. You will be much more relaxed if you aren't freaking out about traffic and running late, and your happy "I'm early" karma will help you start out on a better note.
That kind of time cushion may not always be possible, but think of it as a gold-standard and always build some flexibility into your schedule so that you don't have to sweat and get hypertensive while sitting in unexpected traffic.
There is one stress management strategy that works so well, it simply buries all the others. And it's so simple; you aren't going to believe it actually works until you try it.
Breathe. That's it. Just breathe. But breathe deeply and slowly. Let your breath come in and fill your lungs as far as they go. Take the breath in until your belly expands and your ribs grow, and then let it out slowly, little by little. Do it again, may be three or four times. Be careful to let the air out slowly, or you will hyperventilate. Some people like to visualize things while they are doing this--they think about lavender fields or imagine themselves standing in front of the room while everyone applauds. If you think that requires a little too much imagination at a time when you're trying to focus on the present, just stick with the breathing.
Your body is designed to react to stress in certain ways. It produces more adrenaline and your heart speeds up. You might start to tremble. Your shoulders contract in order to protect your vital organs, and your breath comes faster and shallower. That shallow breathing will make it very hard for you to speak loud enough that other people can hear you. Consciously breathing deeply and steadily shows your body that everything really is okay. This signals your heart to go ahead and slow down. It is impossible to stay stressed out while taking deep, cleansing breaths. This is exactly why breathing is a central part of yoga, and why they teach it to new mothers getting ready to have babies. If people can use it to help with childbirth, certainly it can help you settle down before your presentation.
If it's a very small group and you know everyone well, you can skip this step. But if there is anyone you don't know or who you think may possibly not know you, make sure you do a brief 10-second intro.
Example: A local Chamber of Commerce has a member lunch every month. At each lunch, the President makes sure to state her name and job title as soon as she takes the podium. Later on, each member in turn stands up and introduces themselves. There could be 200 people at this meeting, so it is critical that each member restrict himself to name, company name, and a 10-word power blurb. Listeners count words, and if the member goes over the limit, the audience will actually start to "boo" (in a very jovial manner).
The power blurb is a great exercise in introducing yourself and what you do very concisely. Try it at your next meeting, and make sure you keep it under 10 words!