Start preparing for your presentation as far in advance as possible. Do any necessary research. Speak in front of a mirror so that you can correct any awkward tics or mannerisms. Time yourself with a stopwatch so you won't go over your time limit. Practice saying any difficult words or phrases.
Your presentation should have an introduction, a few main points to expound on, and a conclusion. Your goal is for the listener to have reached a new level of understanding by the time you get to the conclusion. How detailed your presentation is will depend upon the time you have available to speak. Presentations of an hour or more can dig into a topic in depth, while presentations of a few minutes may barely highlight the major points.
It's a good rule of thumb to be at least as dressed up as your audience; for example, if they wear suits, you wear a suit. In more casual environments, select clothes that fit you well and are clean and neat.
A friendly smile and a few words of greeting and appreciation can go a long way in winning over your listeners. If appropriate, you may want to break the ice by starting your presentation with a humorous observation or a small joke.
Keep the tone of your voice clear and firm, and don't let your tone of voice drift up at the end of a sentence unless you are asking your listeners a question. Speak loudly enough so that your listeners can hear you easily. Speak slowly, but with expression, and pronounce each word clearly. Take slow deep breaths to help you stay calm and to modulate your speech.
If it is allowed, enhance your presentation with hand-outs, posters, Power Point, or picture slides. These materials can give your audience a greater understanding of what you are saying. They also give listeners something to focus on besides just the sound of your voice.
If the format allows, finish by asking your listeners if they have any questions or anything they would like to add to what you have said. Sometimes, the give-and-take between speaker and audience can be the most interesting part of a presentation.