It's daunting isn't it. It's one of things that most people are really scared of - it's up at the top of the list along with spiders. So here is clue #1 - most people can't do it or don't want to do it, and they're amazed that other people can do it. If you have notes (and if you're new to the whole idea you probably will have) include somewhere in the margin something along the lines of 'They all wish they could do what I'm doing.'
Your audience wants you to do well. No-one sits in an audience thinking 'I hope the next speaker really screws up', and as such they will be sympathetic. If you're new to doing this, say during your introduction 'I'm new to this and a bit nervous'. It's not a sign of weakness, it's a sign of strength to be able to admit to a shortcoming and to be honest - we're going to know you're new at it, because you'll be trembling like a leaf, so just make a feature of it. So view your audience as a group who are friendly, interested and really keen on listening to what you have to say.
Your audience will doubt themselves before they doubt you. Of course, there are exceptions to that - if you say the Battle of Hastings was 1065, you're rumbled, but that's not really what I am talking about. You're unlikely to get anyone stand up and say 'Actually, I think you're getting confused between version 18.104.22.168 and 22.214.171.124 because...' I mean seriously - who cares? If there are facts you absolutely have to get 100% correct - write them down. If you want to look like a real genius, if there's a flipchart available, take a pencil and write your numbers/bullet points down lightly. No-one will be close enough to see, and you'll just be pulling figures out of your head as far as they can tell.
Set up your ground rules before you start. Questions during or after is an important one. If you're confident enough to take a question, go off at a tangent and then come right back on course, go for it. If not, ask that questions remain to the end.
Timing. I'm guessing you'll rehearse. That's good, but don't over rehearse, since it won't do you any good in the long run. A couple of times tops, just to make sure you know your running order. If you're using cards/notes mark your half way point, and then before you get up to speak, mark your half way time. No point in doing it before, since if the start of your talk is delayed, this won't help and you'll get confused.
Write down or note what you want to say. Then create slides to back it up. There's a whole bunch of good stuff out there on using Powerpoint. This is my take on it. Nothing wrong with Powerpoint - as long as you don't actually need to use it. What I mean by that is that you should use your slides to back up your talk, not use a talk to back up slides. No more than 3 bullet points if you're going to refer to them individually, or if there is lots of data on the slide refer to it generically. For example, if I'm talking about how much data goes onto the web I'll pull out lots of stats and throw them into a slide. And then say 'choose any of the stats on the slide. That's what we're talking about here'. Try and use photographs or images instead of words if possible. It's more interesting for the audience.
Tell stories. People like stories, and the best speakers and writers use them all the time. If you don't know a story to illustrate your point, make one up. Who is to know? Obviously you want to keep within the bounds of possibility and a story that starts 'As I was looking deep into the jaws of the Grizzly Bear those sharp teeth reminded me ..' isn't really going to work. Unless of course that actually DID happen, and if you're capable of thinking like that in that situation you'll also have had enough forethought to remember to video it. Seriously - people video themselves in the middle of earthquakes, the least you can do is take a quick snap of the inside of a bear's jaw for heavens sake!
Hopefully you at least smiled at that. Which was part of my intention - humour is good. I don't know of a situation where humour doesn't help. I've spoken at christenings, weddings, funerals, big conferences, small conferences and so on, and humour always has a positive effect. Just make sure the humour is right for the event!
Don't read from your notes! Key words, bullet points are all you should have, in my opinion. If you have more, it's going to tempt you to read what you've written, and that's never going to go down well. That's what rehearsing is for.
Oh yeah - back to the audience. (You can tell this is just a thought stream can't you!) Forget the 'imagine them naked' since it doesn't work, in my experience. If you choose the wrong person, it's going to be a real turn off and you'll be damaged for life. If it's the right hunky guy or gorgeous woman then you're going to go down entirely the wrong road as well. Pick 2 or 3 people dotted around the room and talk to them. Everyone in the same area will thinking you're talking to them, and it makes them feel good. At some point or other do try and ensure that you've looked all around the room.
What if it all goes wrong? You can prepare as best you can - take the presentation with you on a memory stick, burn it to a CD-ROM, upload it to Slideshare, email yourself a copy and maybe have a printed version. That'll sort out most issues, and should set your mind at rest. If it's anything else - projector dying, powercut, it's not your problem - that's what conference organisers are for. Let them get on with it. Depending on when the screw up happens, maybe apologise to the audience, but you're there to do a job, and if you can't do that job, it's up to someone else to fix it. Having said that, you want to be able to offer something, because you're (probably) being paid in some way. Internet connection died - you'll have screenshots available won't you. Have different versions of a presentation for different versions of the software.
Take water. It shouldn't happen, but inexperienced organisers will forget you need to drink, much more than normal. Nothing worse than drying up (literally!) or coughing. Water is great if you get asked a tough question. Take a sip of water while you madly think 'how the £$%^ do I answer that!'
Questions. Depending on the situation, repeat the question, ask for clarification if needed and give an answer. If you're stuck or have no clue ("Tell me, how do you think the recent release of xyz affects your point?" Umm.....) throw it back at them with 'Yes, a very good question - what's your opinion?' and let them doing the running. When you answer, always ask 'Do that answer your question?'
OK, I'm bored now. I'll leave you with one more thing. It's THE thing. Y'know, the one that you have to remember. The one that is the one ring to rule them all, the key point. Numero Uno. Get everything else wrong and get this right and you'll still have done brilliantly. (Bradley, if you don't get on with this I swear I'll slap you...)
Ok, it's this. People won't remember what you said. They won't remember what you taught them. They remember how you made them feel. If you're enthusiastic, keen, interested and having fun, the chances are very high that they will as well. The most informative, useful and valuable presentations are dead in the water if they're poorly presented by someone who doesn't give a f... er.. flying monkey. Take a look at the really good presenters - Clay Shirky, Sir Ken, Steve Jobs, and see how they do it. They're enjoying themselves, and we enjoy it as well.