I just googled "tips on creating powerpoint presentations"  - I haven't read any of them so I don't know how good/bad they are.

http://www.research.ucla.edu/era/present/

http://catalyst.washington.edu/quick/ppt.html

http://www.geocities.com/~webwinds/classes/powerpt.htm#Tips

I'd start with planning the presentation, analyzing the messages that they want to convey, the audience, etc. Before they even touch the keyboard, know who they are talking to, what they want the audience to do with the message, and then what the messages are, and outlining the information.

Then cover how to transform the messages onto slides. Parallel structure in the bullets. No more than two lines per bullet and then only if absolutely necessary, etc. Talk to them about readable fonts. That projections are dark letters on a light background are easier to read than light letters on a dark background, etc. How to assess just how small a font they can use depending on room size and projection distance.

Then show how PP can simplify some things - slide masters, slide layout, etc. Show the notes page and how to print out the speakers notes, print out handouts with the three-up format (most useful), etc. How to create a hidden slide and how to make sure the hidden slide doesn't show when printing.

Show how to make it pretty - faded back pictures as the background, etc, or elements that show up on each slide. Dear lord in heaven, please stress how bullets that swing in like they are on a trapeze are ridiculous. But how they can make the bullets appear (appear! not fly in) on click or on a timer, and how they can time the show to make them appear automatically in time to their speech.

Then the final session are the really tricky things - how to have a hyperlink that will play a video, etc. Probably tables in PP. How to paste in charts from Excel. (The chart feature on PP sucks, so encourage them to NOT use it.)

That's all I can think of at the moment. Let me know if this is helpful and if there's anythingn else you can think of.