I was in Washington D.C. yesterday for the Parallels Summit. Parallels makes control panel applications for web hosts and BV Commerce is now integrated into Plesk (and soon the other panels). During the summit there were a lot of presentations and the experience of the speakers varied greatly. I don't want to point out specific names but watching the mistakes that were made you could learn a lot:

One speaker moved from slide to slide in PowerPoint by right-clicking and choosing "next slide" from the context menu. Don't ever do this! That's what the spacebar, arrow keys and remote controls are for. It wasn't that the information was poor but the constant "right-click, next slide" was so distracting it was hard to concentrate.

Several speakers had slides that looked like they came straight out of Webster's Dictionary. You know, the book with incredibly small print? Needless to say it was impossible to read those slides so you might as well pull them out of the presentation. Always use large fonts and always go for less information on more slides instead of packing it all into one. Human short term memory can only hold about 7 to 9 items at once anyways and that is a lot of information to put on a single slide.

Another speaker had some slides with a white background, silver and light blue text. Contrast is very important during presentations because projectors will tend to wash out colors that are perfectly readable on your computer display. Pull out a color wheel and pick two colors on opposite sides. Orange and Blue, Red and Green, Black and White etc. 

Scott Hanselman is an evangelist for Microsoft who does a lot of tech demos and has some other great presentation tips.