Oral presentation
Rehearse! Reading your slides nearly word-for-word is the classic boring PowerPoint presentation. So don't do that. Instead spend your time on things like interpreting and giving context for your material. Get familiar enough with your material that you don't need to read your slides.
Engage the audience. Instead of facing the projection screen or looking down at note cards make eye contact and engage with the audience. Don't focus on the instructor – engage the whole audience.
Speak clearly. Speak loudly and distinctly so people can hear you without straining. Common problems are trailing off at the ends of sentences or speaking too fast.
Visual materials
Rehearse! Make sure your materials are readable and free of typos or other embarrassments. Colors that look fine on your monitor may look worse when projected, so rehearse in a room with a projector if you can.
Never use a slide filled with dense, small type (either words or numbers). This is guaranteed to lose your audience's attention.
Use the minimum number of words needed to make your points clearly. The audience does not have time to read and understand detailed explanations. It is not always necessary to use complete sentences.
All your text and graphics must be large enough to be readable throughout the room. This includes labels on charts and graphs. If you are using graphs made by someone else you may need to retouch them for legibility (as long as you don't alter the actual data). The rule is that if something isn't important enough to be legible then get rid of it! You should never have to say "You probably can't see this from the back of the room, but..."
Devote each slide to a single theme. Put a title at the top of each slide so the audience knows the point you are trying to make. Instead of a bland, generic title like "Data" use something more meaningful like "Measurements of growth rate." Use just enough slides - not so many that your audience can't keep up, but not so few that you leave out important information. A rule of thumb is about one slide per minute (more or less, depending on the material).
Choose slide backgrounds so they make your text easy to read. Avoid garish color schemes or hard-to-read color combinations (such as one light color against another or one dark color against another). Consider using a minimalist approach that focuses on your content instead of visual frills.
Conventional capitalization and alignment is easiest to read. DON'T USE ALL CAPS or centered alignment.
Timing
Rehearse! If your presentation has a stated time limit this limit will be strictly enforced just like at a professional meeting. If your presentation runs too long, delete some material and rehearse again.
If you run out of time don't race through the rest of your presentation. Skip some details and go straight to your conclusions.
Mechanics
Rehearse! Work out any technical kinks (like graphics or animations) ahead of time so you don't have to apologize to your audience for something not working.
Ensure in advance that your presentation is viewable. Be especially careful of animation loops. A good way to test this is to transfer your presentation to a different computer and see if it still works.
Did I mention that you should rehearse? You really should rehearse.