I'll give you my biggest three.

Know your subject.

Understand who your audience is.

PowerPoint is but one tool in a good presenters tool belt.

Practice all three,

$.02 worth <g>

Austin Myers
MS PowerPoint MVP Team

Provider of PFCMedia      http://www.pfcmedia.com

Remember that the presenter is your content expert - not the slide. If all
the content is on the slide, why have a presenter at all.  

Consider using "dual coding" coined by Edward Meyer. His research shows that
a headline and graphic only  (on a slide) result in the highest
learning/retention among the audience.

Agree in full with what Austin and Sandy said, but it doesn't matter how
well you know your subject if you aren't comfortable with the content.
Practice what you need to say. Practice answering questions. Practice moving
through your presentation. Practice. Practice. Practice.

    I like this thread--here are a few additional "rules" to follow to
prepare a quality PPT presentation according to the experts.  (I've attended
multiple seminars and conferences on this topic, and now teach the courses at
a university.

-select or create your template carefully:
     If you can find out about your presentation room ahead of time (the
dimming of lights, audience distance from your slides, etc.), that will help
guide your decision of light text on dark background, or vice versa.  

-use a consistent slide template:  
    sometimes the tendency is to spice things up by changing things around
and having a different slide background for each slide.  That's a definitele
no-no.

-avoid too many "bells & whistles":  
    And  related to that, avoid the tendency to flood your audience with a
bunch of bright & shiny objects.  The rule is as follows:  "JUST BECAUSE YOU
CAN, DOESN'T MEAN YOU SHOULD."

-the Rule of Six:  
    Use no more than six words per line, and six lines per slide

-text size:  
    Should never be smaller than 24 pt. if you want it to be legible.  For
things such as the source of a chart or graph, etc., smaller is ok.

-use words and phrases, not complete sentences.  
    Accordingly, no periods at the end of a line, since it isn't a complete
sentence.  This also safeguards against the tendency of some to READ their
slides, instead of give a presentation.  This also helps your audience listen
to YOU and absorb your information, instead of ignoring you and simply
reading your slides.  (For those of us who remember the old cartoons with the
"bouncing ball" at the bottom of the screen that bounced on the words as the
characters would sing, you get the idea here!)

-add a blank slide at the end that's only your template.  
    This signals that you're finished, without having the audience witness
the awkward process that happens when the program switches from the last
slide to "non-slide show" mode.

GOOD LUCK!  Hope this helps!
Julieanne

Here's a couple more:

Avoid reading the charts to the audience.  I've seen a number of presenters
do that--even when they know the material.  It's a flat way to present--and
the presenter ends up facing the screen to read, not the audience.

The charts are in support of the presenter--not the presentation.  In the
Army, there's something called a "PowerPoint Ranger."  It refers to officers
who put ever possible detail on a slide just in case, so they end up with a
chart with 6 point font on it to get everything on it.