Don’t talk too fast. You may want to get your presentation over with, but pace yourself. Otherwise, it'll be hard to understand you. But definitely don't go over your allotted time, or people will start to zone out.
When people hear a speech, they don't usually recall the data afterwards. Try using an anecdote—a quick interesting story—that gets your point across and makes it memorable.
If someone asks a question, remember to be courteous and thank your classmate or instructor for the question. If someone challenges your presentation, your instinct might be to become defensive. But remain calm, take a second, and then give your reasoning for why you stand by your presentation, restating your thesis if need be.
Try not to cross your arms, wring your hands, or clutch them together. You'll seem nervous (which of course you are, but they don't need to know that). Try putting a hand in your pocket or on your hip, or use a hand to gesture, or use one hand to hold (not clutch!) your cue cards. Stand up straight with your shoulders pushed back slightly— you'll look taller, cool, and knowledgeable. If you're feeling confident, step away from the podium. All the great presenters walk around the stage like they own it (think Steve Jobs). And of course there's eye contact...
You want to enunciate your words, but without sounding robotic. Here's how: don't read from cue cards you wrote your speech on, word for word. Take it from me, and my personal experience. You think you're being sly, but everyone knows you're basically reading out loud, no matter how often you try to lift your head up to make brief eye contact. You just end up looking like a bobble head. Try using cue cards with bullet points for each point you need to make, with key words or phrases—not full sentences, or you'll be tempted to read from it.
Not sounding like a robot is where practice comes in. You need to be familiar with your own presentation, so you don't end up with your nose in your cue cards. Trust me; your presentation will seem so much more natural and you'll seem super confident and extroverted. And the rest of your class will be receptive to that, and pay more attention. Don't sweat! Just practice, take deep breaths, and feel free to make an (appropriate) joke or anecdote to break the ice.
What NOT to do
What did you notice about Ross's presentation?
(He was reading from the cue cards in full sentences, which threw off his eye contact and his ability to sound like a normal human being. Even practice won't help that!)