Great post and good comments from others, also.

A couple of points from my experience:

1) Nervousness. During a couple of presentations I've been so nervous I could hardly breathe - the breath was coming in but not getting out again, my voice seemed to be catching in my throat. One was on a presentation course where we were videoed. I had felt like I was dying on stage and I was very surprised to see that in the video none of that came across. Others in the course said the same thing. Strangely this has been a confidence boost - even if I'm dying inside I know that most of the audience won't see it.

On the other hand, (pun intended) anything that you do with your hands will show all too plainly how nervous you are. Brits will remember the famous interview between demon interviewer Jeremy Paxman and politician Michael Howard a couple of years ago. Howard looked cool, calm and collected until he pulled some papers out of his pocket and they were trembling like leaves in a wind. I have been caught out pointing to something on an overhead projector, and also using a light pen to point to something on a screen. Both magnify quivers enormously.

A last point about nervousness: I find I speed up when I'm nervous. I may have practised a talk to fit into a certain timeframe but when I do it for real I get through it quite a bit more quickly. If you've got a certain slot to fill and you finish early, don't be tempted to improvise and pad it out. I've done that and it was a disaster. Better to ask for questions or just finish early and let the audience have a break, even if it's just standing and stretching - they could probably use it.

2) Preparation. The best advice I've had about preparation came from RNZAF instructional technique training. Although the technique is specifically for instructional talks I have found it adapts well to both general presentations and writing reports. This is a top-down preparation technique that involves 5 stages:

a) Determine the Objective of the presentation. What do you want to achieve? Think in terms of what you want the audience to be able to do at the end. Write it down using "action" words. eg Don't write "The audience will understand...". Instead, write "The audience will be able to describe...". Sounds pedantic but it really clarifies your thinking.

b) Determine the Enabling Objectives. What topics do you need to cover to achieve the Objective? Brainstorm and list them down then rearrange them so they're in a logical order.

c) Determine the Teaching Points for each Enabling Objective. Okay, this is aimed at instructional talks but it just means listing the facts you need to get across for each topic. Once again, once you've got the list rearrange them into a logical order.

At this point you've got your presentation. No need to write it down like a speech, word for word. Just list down the topics with factual bullet points under them.

d) Determine the Method of Presentation. What's the best way of getting the info across? eg a demonstration, a discussion (with participation from the audience), a one-way talk (you talk, they listen). This depends not only on the subject of the talk but also on the situation - are you showing a group of high school kids how to change a car tyre or are you presenting a scientific paper; are you talking to half a dozen people or 200?

e) Prepare your Presentational Aids. eg Powerpoint slides, handouts, animations on a laptop. Do this last for two reasons: i) The important bit of the presentation is the information you put across, not the bells and whistles. If you're pushed for time which is better - to have a talk without handouts or handouts without having an idea of what you're going to say? ii) Your talk won't depend on the presentational aids so if something goes wrong with them (eg no laptop - see comment above) you can still present your talk.

Some further points about preparation from my own experience:

i) Know your subject before you start your preparation. If you can understand the subject and hold it all in head it makes it so much easier to determine which topics you need to cover, and what the teaching points are.

ii) Preparation really is the key and you shouldn't skimp on it. In my experience the preparation time should be at least 4 to 6 times the length of the presentation. For short presentations of half an hour or less expect to spend even longer, proportionately, on preparation.

iii) Practise. If you use the list of topics and bullet points that I mentioned above, rather than a written speech, you won't ever sound like you're reading your talk because you aren't! But you do need to run through the talk a few times to yourself so you're comfortable with it.