Before
Do you want to inform, train, persuade, show your ability, entertain or demonstrate?
Do you aim to get ideas or feedback from the audience, as well as sharing your ideas? If so, how will you do this?
Is your approach formal or informal? Does your talk include a PowerPoint presentation, a demonstration or is it a discussion?
Introduce yourself. This may not be necessary to colleagues. To possible future clients, it will be important to give key details.
What's the purpose of the presentation? To inform, persuade, demonstrate?
Give your audience the main points of your talk and the sequence so they know the structure.
You need 100% attention of the audience. Maybe you need to tell them how long the presentation is, tell them if you will give them notes at the end.
Tell them when they can ask questions.
