Research! Know your topic not just well enough to give the presentation but that you can answer any questions that people ask you at the end. It'll pay off to take notes or at least save the helpful books and websites you took when you make your presentation, so that if you can't answer the question you can at least point the person in a helpful direction.
Figure out who you're going to present to (you might need to find a location first - if it's at school or work then you know who your audience is). This will help you when you prepare your presentation - some information is going to be obvious to the more advanced audiences while some will be too hard for younger audiences to understand.
If you haven't found a location and time yet, do that now. Consider when and where your audience is likely to be. Make sure to leave yourself at very least a week, preferably two, to prepare your presentation and publicize it.
You'll need to do steps 5&6 at the same time in the weeks before the presentation - don't leave them until the last minute, or even the last couple of days!
Put your presentation together. If it's simply a speech, type the whole thing up, or at least just write detailed bullet points down that you can use at the presentation. Remember, though, to try to keep it as interesting as possible - try to make it interactive and/or short. If you want to make a powerpoint, be sure to check and make sure that there'll be a computer and a projection screen at the site of your presentation. If there will, go ahead and make it. Try to add at least one relevant picture per slide, and no eye-popping backgrounds, fonts, or animations. Don't put too much text on each slide - try to stretch it to two or three slides if the font size has to be small for it to fit on a single slide. If you're doing a powerpoint, don't worry about typing up a prepared speech unless you don't think you'll be comfortable without one.
Publicize. Put up posters in places that have been okayed for you to do that. Send out flyers. Make announcements at lunch, assembly/meetings, or other available times. Try to make your posters and/or announcements different from others, and be sure to tell people why it'll be worthwhile to come.
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