Pretty much, the answer to this is: common sense.
Speaking: Make sure that your voice is loud enough for everyone to hear you clearly. Speaking slowly is much better than speaking quickly, and take the time to articulate your words. It is better to cut material out from your talk than to rush through it. Don’t shake or fumble your words when you speak, try not to studder.
Speaking Without Words: Let your voice convey authority, expertise, and obedience. I have seen too many students try to give a talk that had a soft tone to it and then by the end, the listeners are not paying attention at all and have erupted to talk over the speaker and amongst themselves. Don’t be nervous, but be calm, collected. If a question is asked and you don’t know the answer, don’t panic! Tell the truth, you don’t know, or defer the question to a later time (“Can you come talk to me after this lecture and we can discuss it then, please?). Be passionate, avid, excited about your subject, and your listeners will be too!
Movement: Don’t be afraid to move around if it feels more natural to you, however remember that it is not a magic act, so you should try to remain up front, instead of wandering through the audience. Hand motions and body language can be a great help in conveying your idea. Don’t be afraid to point or move your hands towards relevant sections of your projected notes (if you have them).
Eye Contact: Look at your audience in the eyes, don’t skip any corner or area of the room or focus on any one particular section for too long. This should also help calm your nerves as you speak.
Take a humor break! Good speakers use a guideline of three minutes of a (preferrably humerous) interesting side trail for every twenty minutes of speaking. That is, you should tell a joke, or a related story every twenty or so minutes. Listeners can get tired, distracted, or bored very easily, and this is bad.
Projector Slides: This is a whole topic all on it’s own, but there are several common sensical things you should know. Don’t cram too many words onto each slide, and try your best not to have your slides be pages of main points, sub points, and sub sub points. Using pictures and diagrams are excellent conveyers of information, after all, a picture is worth a thousand words. Slides are not narrations of your talk, instead they are visual aides, helpers.
Preparation: Be prepared! In your mind, know and be aware you will be giving a talk. Try to think of some questions your listeners might ask and review their answers. Bring water if it will be a long talk. Show up early, have all of your materials (slideshow, handouts, etc) ready to go. Don’t be flustered, frustrated, nervous, or grumpy, your audience will pick up on it and imitate you. Practice, practice, practice! Practice your speech aloud, ask your friends if you can practice it to them, take advantages to practice public speaking, and practice in multiple settings.