I am by no means an expert at public speaking, but over the past few years I've found myself in front of an audience more and more often. Some times I've excelled, sometimes I've bombed, but I've managed to learn a few things along the way. Eat before your presentation Especially if it is a presentation centered around a meal, like a "lunch and learn" or if you are the speaker at a dinner. Normally, you'll be scheduled to speak at around the same time others are eating. Even if is a casual setting and you'll be dining with your audience, you don't want to look like a glutton. Your audience is there to hear what you have to tell them, not watch you eat.
Eating beforehand also ensures that you don't spill anything on your shirt.
More water, less coffee Coffee gives me the jitters, and I tend to speak too quickly and excitedly. Water keeps me hydrated and my mouth moist so that I can keep on talking.
Know Your Material Your audience will be able to smell bullshit more easily than fear. If you don't know your material very well, then you shouldn't be speaking about it. If you understand your material well enough, no amount of distraction, nerves or difficult questions will throw you off.
Engage your audience Look them in the eye, ask them questions, make them feel like they are part of a conversation rather than being lectured at. Look around at different people in the crowd (rather than at the back wall, as I used to do) gives you a better idea about who is paying attention and who isn't so that you can measure the level of information getting across. If all you see are glazed eyes and people praying into their Blackberries, you need to be doing something different to get their attention.
Make sure your fly isn't open and that your shirt isn't tucked into your underpants Seriously. It takes two seconds to check. (Hilarious anecdote related to this tip available upon request.)
Any other advice?