One of the biggest mistakes you can make when presenting is to be uneducated in the subject matter, whether in part or in whole. People often think that they can gather together a few basic points about the subject matter and get through the presentation. However, this is often transparent and results in a lowered grade or less respect from the audience. Prior to the presentation, conduct the appropriate research whether that means going to the library, researching on the Internet or conducting interviews. Write comprehensive notes when conducting research so that you can read over the notes later and organize your presentation. When preparing for a presentation, "dig deep" for facts and information.
If you are able to choose the topic for your presentation, keep in mind the audience. Presenting information to one audience that's really meant for another won't have a positive impact. If you're not able to choose your topic, try to find some aspect of the topic to relate to the audience. Additionally, base the way you interact with and speak to the audience on the age group. Typically, you'd speak to students of elementary age in a more fun, interactive way. High school students typically desire a direct presentation with less interactivity. For students in college and beyond, the tone is typically more business-like with interaction on a question/answer basis.
Knowing the environment in which you will be presenting will aid with any props or technology you may want to use. Find out if there is a projector available, if there is room for flip charts, posters or model dummies. For instance, if you're presenting about CPR and you want to bring in a dummy to demonstrate, find out the setup of the venue ahead of time so that you can appropriately prepare. The size of the room will also drive whether or not you use posters versus a projector. Larger rooms require magnification.
It's always best to have some sort of beginning, middle and end to your presentation. However, this doesn't mean that your presentation has to read like a paper. Be creative with your presentation. To gain the attention and interest of the audience, begin by telling a story that relates to the topic and the audience. For the middle, or bulk of your presentation, section it into 15-minute increments if you're presenting for at least 1/2 hour. At the end of each 15-minute increment, provide a synopsis of the material just covered, field questions or conduct some sort of review "game" or exercise. Conclude by providing a general summary of the presentation. If you feel that another story will drive your presentation home, share it, but be sure to tailor to your audience.