This article from the Toastmasters web site is appropriate for most speaking and presenting situations, not just impromptu speeches. The bullet points of the performance-related issues:
-
Greet the audience.
-
Don’t say anything that lowers the audience’s expectations.
-
Buy yourself time, but be careful not to overdo it.
-
The more alive and original you are, the better your performance will be.
-
Sell your idea to the audience.
-
Practice!
-
The audience is in the same boat as you.
The last tip is especially helpful to remember in the classroom environment.
In case you’re wondering, Table Topics is a Toastmasters exercise that occurs at every meeting. Members give off-the-cuff impromptu speeches on a particular topic.