Know your topic. If you don't do your research right, you may say the wrong thing or forget some important aspects.

Use key phrases in your topic. If your topic is vast, choose just a couple key points to talk about and emphasize on them.

Don't spend too much time on one slide, make it only a few sentances. Not one that will take the audience 5 minutes to read.

Limit your number of slides. If you have too many you might find yourself rushing through them to get done, and then the audience will be paying more attention to your slides than you.

Make your slides easy to follow. Contrasting colors and fancy fonts should be avoided, otherwise your audience will spend their time trying to figure out what the words say.

Don't use a lot of animations and transitions, because then your audience might not even pay attention to the message of your presentation.

Don't put in your whole speech on the slides. This is a common mistake that many students make. You want to just put a few sentances on your slides, and have the rest or other key points on note cards.

Check the projector to make sure it's working right beforehand. If you don't you could have to make your audience wait for quite a while if your having technical difficulties.

Don't use all capital letters. Even if you are trying to emphasize something, using all caps is a way of shouting.

Ask people if they have any questions in the end. Then answer them accordingly as best as you can.