The most important part of impromptu speaking are your Thesis and Argument.
It's all about the subject.
The trick to Impromptu speaking is knowing how to adapt your examples to your topic. Notice that it's not about the examples, it's about the topic and the adaptation. A wide variety of examples definitely helps, but if you know a single example really well you can make it work if you try hard enough.
For instance, say you're giving an impromptu speech on the following quotation:
"Greed is good."- Wall Street
The Thesis Statement.
You could just say 'Of course it's saying greed is good,' and go on to agree or disagree with that. That would be your thesis statement.
A better thesis would go more in-depth and say "The quotation is saying that 'Greed, meaning wanting more than you need to survive, is good' Or 'Greed, unquenchable thirst for more, is good.' Make sure you define ambiguous terms like 'Greed' or 'Honor' or 'life.' Summarize.
The important thing in the thesis statement is to clearly articulate your interpretation of the subject. Note that it is Not about the 'correct' interpretation of the subject. It is about whatever interpretation works for you, but it should be true. This is much more important with more ambiguous quotations, but true at a basic level. Every quotation is open to (mis)interpretation. If you make your thesis statement interesting, your speech will be interesting.
Then you agree or disagree with your interpretation of the subject. This is usually combined with a sort of pre-preview of your main points; make your argument while stating your (dis)agreement. For example,
"So we need to look at today's quotation, "Greed is Good," from Wall Street. This quotation claims that Greed, an unquenchable thirst for more, is a positive trait. This is true because greed allows us to ignore rationality, and because greed allows us to empathize with other people's struggles."
Make clear assertions here. Do not say 'First we'll look at why greed is good, second we'll look at why greed may not be good.' The audience should know exactly what you're going to say. Greed lets us ignore rationality, greed allows us to empathize, greed is good. Simple, clear, intriguing. Empathy through greed? Say wha? Now I'm interested.
Go to www.quotationspage.com and get a few random quotations. Don't use a stopwatch for this part, but look at the quotations, notice the ambiguous terms, and summarize it as quickly as possible.
Example: "Action is Elegance"- William Shakespeare
Elegance, Action, and The relationship between the two all need definition. Good quotation :).
Action is taking immediate steps to achieve your goals. Elegance is being stylish and powerful at the same time. Taking immediate steps to achieve your goals is the best way to be stylish and powerful at the same time. Bam, thesis. Again, it's a good impromptu quotation because it's short and yet wholly ambiguous. Thank you, Shakespeare.
Try running this same quotation five or six times and you'll see how a finals round looks: everyone makes an immediate, probably different, interpretation of the exact same quotation.
Tomorrow we'll look at the second most important part of Impromptu, the Main Example.