As shocking as it may seem, public speaking consistently ranks as the top fear for Americans, beating out legitimately deadly items like fear of death or cancer. In many ways, it makes sense biologically. Humans want to feel like a part of a group, so there is an innate fear of slipping up and being ostracized. After all, being ostracized meant exile and death in the caveman times.
However, we're not cavemen anymore, and the fear of public speaking is an unnecessary one in this day and age. Plus, learning how to effectively and confidently convey your message to other people is very important in many facets of life, perhaps most notably as a marketable job skill, so don't think that this is something that just goes away after that mandatory college class ends.
Practice, Practice, Practice
The most important thing that you can do to make sure you deliver an effective speech is prepare well and practice it beforehand. This does NOT mean just scanning through your notes or PowerPoint slides.
Instead, put on your PowerPoint presentation and stand next to your computer monitor the same way that you would a projector display in front of your audience. Figure out what you want to say to introduce your message, and how you want to conclude the speech. Set a stopwatch on your phone and be sure to time yourself too to get an idea of how long you will be talking. As you are doing your first few practice runs, make mental notes of the parts of your speech where you stutter or feel unsure of what to say. Then before the next practice-run, think of ways to correct these parts of the speech and make them flow better.
Do at least half a dozen practice runs, and more is even better. Continue practicing until you run through the whole speech smoothly with no slip-ups. At that point when you get up there to do it for real, it won't feel difficult. After all, in your head this will be just one of the many times you have already given the speech. It's nothing new or scary, it's familiar and comfortable.
Know More Than You Let On
Imagine you were asked to talk for 5 minutes about a subject that you know a lot about. Maybe it's a hobby. Maybe it's a particular movie or TV show or book. Would it be easy to talk for 5 minutes? Of course!
Let's say you are up talking and realize you have only fulfilled 4 minutes. This is not an issue for you because it's a topic you know so well. Therefore it's easy to summarize or fill up the next minute with relevant anecdotes.
You should always have more information than can fit in your speech. It gives you one more thing to blurt out if you freeze up, and it may help answer a question someone has after you are finished speaking.
Many people who are not comfortable with public speaking will talk much faster when they are up in front of others. Often times, they don't even notice that they are doing it!
This is a behavior you want to stop. It's 100% okay to have pauses in your speech. A well-placed pause is great for emphasizing something and making the audience mull a point over in their heads. It also is much better to have a pause than an unnecessary vocal filler (um, uh, err.)
In addition to benefiting your audience, it will also make your speech feel much calmer. You'll often see people completely out of breathe after they are finished speaking. You don't need to be like that! Go watch politicians speak. Those guys and gals are professional public speakers, and they take pauses ALL the time, both for dramatic effect and so that they can swallow or catch their breathe.
Silence is not a bad thing, and your pauses are usually much briefer to your audience than they are to you. For you as the speaker, a 3-second pause may feel like an eternity of awkward nothingness. From the audience's perspective, this is just natural speaking and they don't even notice it.
Don't Forget the Introduction and Conclusion
Believe it or not, most of your audience will forget most of what you say almost instantly. It's information overload.
A lot of people unfamiliar with public speaking think only of the body of their speech. The logic is that since the body is the "meat and potatoes" of the speech, that's what everyone is going to remember. And in a perfect world, this would be true. Unfortunately, humans really aren't logical.
Most of your audience, unless they are very intent on soaking in your every word (and let's be honest with ourselves, most people aren't that attentive) will remember your introduction and conclusion better than the body. This mean seem unfortunate, but it's important to look at the positive side, something professional public speakers know very well: you can make a mediocre speech look awesome by just ensuring your intro and conclusion are memorable. It's like a perfect cheat code!
For your introduction, the most important thing you can do is get people's attention. There are a few ways to do this. You could ask a question, tell a joke, show a picture or video clip, etc. It really doesn't matter what you decide to do. In fact, it doesn't even have to be all that relevant to the body of your speech. What does matter is that you take people's attention away from their cell phones and direct it towards you.
For your conclusion, what you DON'T do is actually the most important factor. Most people flat-out suck at ending speeches. They say things like "And that's all" or "And that's my speech" or, the worst culprit of all, "And... yeah...." followed by an awkward shuffling off the stage. Avoid doing this like the plague. Your audience is smart enough to realize when your speech has ended. If they aren't, you leaving the stage and taking a seat among them will be a pretty good indicator. Either one, don't say anything. Summarize your primary points, have a half-decent final statement, and click off your final PowerPoint slide. They'll clap, and you can feel proud knowing you just gave a better speech than 99% of the human adult population.
Ultimately, the key to successful public speakers really is being relaxed and comfortable. Once you accept that it isn't a big deal, it will cease to frighten you. And... yeah....