If you get nervous about speaking in front of an audience then consider yourself entirely normal. Fear of speaking in public regularly comes high up in surveys of human fears. Unless you do it everyday, presenting takes you out of the 'comfort zones' of daily life. It is the feeling of exposure and uncertainty that leads to the sweaty palms, butterflies in the stomach and shallow breathing.
But feelings of nervousness are essential to our body's preparation for a new challenge. We can't function without the good nerves. They give us energy, expectation and focus. The problem is not the nerves, but the thinking we do about them.
Here are some of my notes on nerves and presenting.
Nerves? What Nerves?
'You were nervous? Well, it didn't show.'
Nervousness usually feels worse than it looks (that's if people notice at all). Your image of yourself may be worsened by nerves, but it probably does not look that way to others. Your sweaty palms and trembling left leg are probably invisible to an audience, even though you may be very aware of them yourself. So your nervousness might not be as bad as you think.
Change your Thinking
Live through your nerves, accept them, know the signs of bad nerves, and change your thinking about them. You need to put something between the nervous symptoms and the negative thinking that they can lead to - if you let them.
Try to focus on your material - not the detail but the 'big picture' - or think about something else entirely. 
I had a colleague who always read a page or two from a novel before presenting. This was his way of relaxing - by NOT thinking about his presentation in the moments before it began.
Try thinking about any everyday thing that is not too demanding: What are you going to cook tonight? What shopping do you need? What book are you reading at the moment? Or think of your next holiday.
It's not about You
Although your nerves may try to tell you otherwise, the presentation is not really about you. It is about the topic. You need to focus the audience's attention on the topic and not on you. So begin with composing yourself so that you can direct the audience's attention to your material.
In my experience, audiences are supportive of people who are nervous. The audience is not your enemy.
Think about your audience as your ally. It is not you vs. them. Remember that your listeners want you to succeed. They are not there to trip you up.
Relax
Do some deep breathing, holding the breaths for a few seconds and then letting them out slowly (this helps to make the body look relaxed, even if it doesn’t necessarily feel relaxed). Relax your shoulders. Keep your hands still or do something like reading or making notes.
Start Slowly
Allow yourself to speak more slowly than normal, especially at the beginning, so you can collect your thoughts. Look at people and establish a rapport with the audience, by accepting them into the space that you are in charge of: your presentation.
If you read from a script, look for an opportunity to break from your script early on and talk directly to the audience for a moment.
Forgive Yourself and Move on
Everyone makes mistakes and there is no perfect presentation. All human communication is full of small breakdowns, glitches and repairs ('I'll say that again').
Be forgiving of yourself. You may forget something, make a mistake, cough, forget a word, or lose your bearings momentarily. Don't panic at these moments. Stay calm. Don't let them destroy your presentation. It's only one moment.
Don't let yourself be distracted by individuals in the audience who might give you a hard time while you are talking or who constantly interrupt. If this happens, insist on taking questions at the end. Also, don't be distracted by unusual behaviour in the audience. Audiences are, after all, human.
Once somebody in the front row fell asleep and started snoring during an academic presentation I was doing in Oslo. I managed to wake him up by quoting him and emphasising his name loudly. But really I should not have taken any notice. He was just jet-lagged. The rest of the audience, thankfully, did not fall asleep.
Prepare
Go to the room early and make sure you have everything you need (projector, memory stick, paper, water). If you have to use a microphone, test it. Look for wires and other obstacles to avoid.
Plan where you will put your materials and where you will stand so the audience sees both you and your resources.
Don't panic if technology breaks down. Be ready to talk freely if this happens - the audience will be on your side.
Take water breaks if you need them, ideally at transition points or when people are looking at something on the screen.
And enjoy..
Try to enjoy your presentation and convey interest, enthusiasm or confidence, even if it's a very serious topic. This will relax you and help to get the message across more clearly.
