Talk and behave the way you usually do.
Talk about subjects that you understand:
If a subject is outside your competence – Keep quiet. Do not try to look like an expert on everything.
Prepare, and be prepared:
Write out a full set of notes which can easily be read at arms length. If you use notes don’t hide them – make them obvious – they add authority to your speech.
Be aware of contrary arguments to yours and prepare responses to them.
Base your arguments on facts:
Avoid hearsay and exaggeration. Illustrate your arguments with concrete examples which can be easily proven.
Vary the speed of your delivery:
In normal conversation silence plays an important role. Don’t be afraid of silence; it can be a powerful method of emphasising your point.
Expect to be nervous:
If you are not nervous before your speech then you probably do not really care about the topic.
In most cases the only person who knows you are nervous is yourself.
Look at your audience:
Develop eye-contact with the people who are listening to you.
If you become shaky then look at a friend or a not threatening person until your confidence returns.
You do not learn to ride a bike without practice first. The more times you speak the better you will become and the more confident you will feel