There's an interesting meme floating around Science Blogs, how to give a talk. There's a nice video too. Although they concentrate on science, this advice fits to any discussion. I suggest you read their entries before continuing here as I refer to some of their do's and don'ts.
I divide it into three sections: Preparation, Visuals, and Delivery. There are two ways to approach it, Dr. Jekyll and Mr Hyde techniques.
Practice before the talk! Recognize that the audience will follow the speaker's eyes. If you're staring at your computer screen, that where the audience's eyes will be too. So your cheat sheet is just a list of ideas which you want to cover. This way you can maintain eye contact with the audience and "float" using your eyes to direct the audience's attention. If you're looking at the screen they're looking at the screen.
Know your audience and prepare accordingly. Too many times I've had guest lecturers come in and talk way over the head of the students. You must use a vocabulary they understand and deliver it in an appropriate manner.
Work on pronunciation. I have extreme difficulty saying the word "ubiquitous," and will excise it from my lectures. If you have the same problem, do as I do, simply break open the thesaurus and find another word. Watch your speech patterns, and work to eliminate "OK," "you know," and other figures of colloquial speech. ("You understand" is a good substitute for "you know.")
Don't! Wing it and you'll sound like a pro! Don't read a book or this post, just play it by ear. Hopefully you have a tin ear.
Ignore the knowledge level of the audience. Assume they know everything you know, have read every book you've read, come from the same neighborhood you lived, visited all the sites you've been to, and generally don't need to attend this talk. Introduce subjects without background information, the more complex the better. Best of all use a foreign language, especially obscure dialects.
Don't practice saying difficult words then mispronounce them throughout the entire talk. Better yet, use multiple mispronunciations. Better yet, use trite phrases repeatedly, Better yet, mispronounce repeated trite phrases. Better yet...
Use a sane color combination. I dislike bright white screens so my backgrounds are colors. However, I also use text boxes so that I can have sufficient contrast. Don't use complementary colors, they hurt the eyes as much as bright white. Standard fonts - Serif for titles and headings, sans serif for text. No more than 5 lines per slide if you're in a big hall (75 people?) as students in the back won't see it.
Few if any animations. They're OK if you want to introduce comic relief or make an impact, but must be used like you would cayenne pepper - with great care!
Provide sources or names the audience will recognize. Don't read every source, just let them know where they can find the information you're delivering. Most Art History types will recognize Vasari as the author of "Lives of the Artists," a few will know Panofsky, and fewer still understand Mieke Bal.
Comic sans!! Use obscure fonts, especially script, gothic / olde English and italic versions of them. Wing Dings can really liven up a slide. Write your PowerPoint slides on a Mac then present it on a Windows PC. Be sure to use Mac only fonts like Linotype or Helvetica. Use lots of bullets too! Pack that slide so full that even you can't read it!
Animate to the point that the computer crashes. If you don't know how, then indiscriminate use of bold can stand in for annoying animation. However, NOthing beaTs wierD CapitZation and, stRAnge(!?!) pUncTuati0n to make.it.illegible.
Cite obscure, preferably nonstandard publications and sources. It's difficult in the education setting but if you can violate copyright and trademark law, so much the better. If you can't do that, then don't give attributes, make them guess where to find it.
Prepare the audience. Tell them when questions should be proffered. Can they just "popcorn" them, should they raise their hand, should they write them down and ask at the end. Otherwise you'll have dead silence and a distracted audience.
Don't surprise the audience and stay on topic. Surprises tend to overshadow all other content, rambling confuses them. My first slide after the title one is "4 things you will know after this lecture." At the end of the lecture, I bring up each of the things on separate slides to drive home the point(s) of the lecture. I always draw test and essay questions from that pool of those things. I try to keep it down to 4 things because I work with lower division undergraduates (freshman and sophomores). See the point about knowing the audience.
Our department's mantra is that slides used in the lectures should be the visual argument, and your voice is the textual one. That said - don't read the slide! One exception - if you have a long quote which you want to read. I read Procopius' description of Theodora, a racy and slanderous passage from Secret History, and it always excites the students.
Don't tell the audience when to ask questions and then they do, go ballistic! Belittle their knowledge level or opinion. Make them as uncomfortable as possible - frightened is the best possible position. If you're packing heat make sure they know you're not only willing to use it, you're likely to use it! Extra points if you can get them to leave puddles in their chairs.
Contradict your visuals. If the slide is blue, tell them it's green. Doing this gives you the chance to go ballistic when they question your text. This goes in the behavior category but what do you know, where did you learn this, you wanna get up here and taLK@!@ How abOut you just leave now cause yOu're faIling thIs class Now!