Preparation and delivering the talk are both important, but how to do it properly? Jonathan Shewchuk has a good piece of tutorial on how to give a technical talk. He mentions couple of good points – including minmize your text in your slides, what font face should you be using, how you should organise the logical flow for your presentation, how to speak clearly and precisely, how to close your talk etc:
Speaking. Good speaking is all about rhythm. The most important part of speaking is to choose a few key points in your talk where you wish to bestow extra emphasis, and then decide how you will verbally emphasize them. I sometimes do this by speaking with a particularly slow and deliberate voice; and I sometimes do this by saying outright, “Here’s the most important idea in this talk.”
Sometimes silence is particularly articulate. One of the best (and most underused) speaking techniques I know is to leave a long pause right after making a key point. Let it sink in.
It’s important to give yourself permission to take as long as you like to think of what to say next. There’s no hurry, no need to fill the spaces with sound. The audience is too busy trying to figure out what your slide means to care how long it takes you to think of the next sentence.
You must extinguish the utterance “Uhhhhh” from your vocabulary. Vocalizations like “Ummm” are a half-conscious attempt to pin down the audience with a stream of sound. Remember that they’re not going anywhere. When you don’t know what to say, be silent and think patiently.
The most common type of bad speaker I see is the one who speaks at a uniform speed, never slowing for emphasis, always seeming rushed, never leaving pauses, one slide running monotonously into the next. Figure out what it takes for you not to be that person.
Giving an Academic Talk – [Jonathan Shewchuk]