From a blog I wrote. Please note that I've done many, MANY PR jobs, and I've also been a teacher and like to do speeches and debating in my free time.
Always go first for presentations and speeches. I know that sounds terrifying and silly, but trust me. The longer you leave it, the more tension that rises. This will lead to more mistakes, and even if you have really good points, you'll be let down by inner-torment. Moreover, the longer you wait, especially in the case with the markers, the less concentration your audience will have. The markers will award less marks as they will be bored, and the students "listening" to your speech won't care. That might sound good, but it means there's no point for you to speak. They might even hold it to you if you make them stay there for a really long time.
Your voice is a weapon. Be loud. Be confident. Speak at a nice easy pace. Interestingly, almost all people who do a speech speak at twice the speed of their practice runs. If you really must, you can try centre yourself, as if you're in a small room with just yourself. Most important job of your voice isn't just to communicate information, but also to make people excited. You need to break the ice, and combat awkwardness. By not being one of those boring people, and by using inflections, exaggerations and other vocal tools, you can make people really care what you have to say.
Throw in a dash of comedy if you can pull it off, but don't if you can't. Comedy has very little do with the strength of your jokes. It's all about the atmosphere and your timing. If you can't nail the timing, and if you aren't lively enough to melt the awkwardness in the room, your jokes will become cringe-worthy. That said, having good jokes will absolutely increase audience retention, and should make your markers feel a little more inclined towards your presentation. If you do put in jokes, make sure to only give a very brief laugh (don't go on and on forever, because it soon becomes painful to watch), and don't overload your speech with jokes. There needs to be serious content in there somewhere.
Don't overly prepare and memorise your speech. What you'll end up doing is, in the event that you miss a line, panic and screw yourself over as you rush to find where you were, nervously throwing around paper and being very awkwardly quiet. To reiterate, don't memorise your speech. Instead, memorise the content, and know it well enough that you could speak about it in your sleep. Therefore, if something does go wrong, you should still be able to discuss the content without having to scramble to figure out what line you missed.
Don't hide on stage, and stay still. Be relaxed. Your body language is as important as your speech itself. Just calm down, stand in the centre of the stage and keep your legs still. Don't slouch too much, just give just a bit of lean to show people you're comfortable, and they should be too. Use your hands as tools of expression, to show what you're speaking about. Also, remember your facial experiences, and use them to your advantage. Don't be sitting or stand behind a podium, unless you're sufficiently taller than it.
The less you rely on palm cards, the more your audience will care. I don't use them at all. Your audience didn't come for you to read to them dry content. Furthermore, if you're looking at the palm cards, your voice won't be directed at the audience and so people up the back won't hear you.
Don't put ANY words on your Powerpoint presentations, except for presenter notes. I rely on presenter notes to keep me up to speed with what I'm talking about, but all my slides are just visual stimuli that relate to what I'm speaking about. If the audience sees anything to read, they won't listen to what you have to say. Force them to listen to you.
