About the audience

You should definitely know the following things before you give a talk. Prefably before you prepare the talk:

Who will be listening to your talk?
What does the audience expect?
How many people will be there?
Do these people have to be there or do they have the choice?
How much do they know about your topic?
If your talk is part of a larger meeting, how many talks did the audience already hear?

If you cannot answer these questions, do some research. Ask the organizer, or the audience itself.