You must establish credibility in your speech to persuade your audience that you are correct. Include statistics in your speech. For example, if you believe that cars should be run on electricity and not gas, write specifically about how much pollution gasoline creates in a year. Perhaps you are arguing that downloading music on the Internet should not be free. Include facts that show the damage that such practices cause the music industry. Cite credible sources in your writing to back the facts you present.
Write a position statement, which also goes by the names of thesis statement and argumentative proposition. Within the first paragraph, clearly write out your opinion in one or two sentences. Explain the context of the argument, as well as your side of the argument. For example, you do not want to say "People download music illegally." Instead, you would want to write "People who download music ultimately wind up severely hurting the music industry."
Appeal to the audience's senses of reason, ethics and emotions. Write at least two or three examples or anecdotes related to the main statement to promote reason. As far as ethics goes, use language that shows that both you and your position are fair and trustworthy. Use positive statements about what should happen, as opposed to negative statements that attack. This tactic also blends in with the emotional component. For example, instead of saying "People who download music are bad," make the argument that, "People who download music have not considered the fact that money is taken away from the artist."
In your writing, you must dedicate a paragraph or so to the objections the opposing side could make against your argument. Explain a couple of the objections that could potentially arise. However, then go on to explain why you believe they are wrong. If a potential objection that arises is that people believe musicians have enough money anyway, you could write that such a question is not for others to judge. In any case, you will have addressed objections before they even arise.