Research your topic well. You might have to go to the library, or you may be able to research the subject online. After you speak, you might also be asked questions. If you appear to be unprepared to answer those questions, or if you demonstrate only a shallow knowledge of the topic, you will lose credibility.
Summarize your research in three sentences or less, and write the sentences down. These are your main points. Most people cannot remember more than three points. If you must make more than three points, provide a handout that your audience can follow as you speak. Your main ideas should be in bold print.
Outline your talk. Traditional speeches have three parts: an introduction, a body, and a conclusion. Use your introduction to entice people to listen, and to establish rapport with your audience. Consider thanking them for giving you the opportunity to talk. Your introduction should take less than a minute of your talk. For the next two or three minutes, develop the ideas you summarized earlier. This will be the body of your talk. In the last thirty seconds or so, wrap up your talk by briefly reiterating what you have said, and why it matters.
It takes most people between four to five minutes to read two pages of double-spaced twelve point font, so if your entire talk is a little shy of two full pages, you should be on track. Many people write one paragraph for their introduction, and one paragraph for their conclusion. Allow one full paragraph per idea in the body of your speech.
Decide how extemporaneous you will be. Just because you have written a speech does not mean you have to read it. You can read your speech, you can write notes on index cards and unobtrusively use them. or you can memorize your introduction, body and conclusion. All three methods have their merits, so weigh your options.
Practice your speech in front of a friendly, but honest, audience. Ask for constructive criticism and suggestions. When first beginning to speak in public, many people have annoying mannerisms of which they are not conscious. Such distracting habits include throat clearing, saying "ummm..." in between sentences, speaking too quickly, or involuntary body movements. It may also be helpful for you to practice in front of a mirror. If there is something you need to avoid saying or doing, write a reminder to yourself at the top of the pages of your speech.