Basically, an extemporaneous speech is one that is based on research and data while persuading the listeners to join their opinion based on the presented research. In American schools, the extemp speaker is allowed to choose between various topics and then use thirty minutes to prepare for the extemp speech using newspapers, magazines, books, etc. After this, they give a seven-minute extemp speech on the subject. Usually the topics are about economic matters or foreign/domestic policy.
To create a good extemporaneous speech, the first thing you need to do is to either break the ice or grab the audience's attention. This means that the beginning of your speech must be exciting or engaging. After that, you need to create a thesis that states your speech's intent. While this is only one or two lines, your entire argument depends on it. After your extemp speech thesis statement, you need a small period of clarification to elucidate your position. You have to show your audience that you have a full understanding of your own thesis and the message you intend to convey. Then you need to create a small preview section. This is a sentence or two that describes what you are about to tell the audience.
Now comes the body of your speech. You start this by making your main points and then providing evidence to support them. Show your reasoning so that you may add it to your evidence to solidify your proof. After this, explain how your proof relates to your thesis.
These suggestions make up the barebones of the seven-minute extemporaneous speech. Just make sure that in closing you fully express your thesis statement in clear terms and tie up any loose ends about how your proof relates to the thesis statement.