Lifehacker has an interesting post on Harvard cognitive scientist Stephen M. Kosslyn and his four suggestions to improve Powerpoint Presentations.
The Goldilocks Rule
Present the "just right" amount of data. Never include more information than your audience needs in a visual image.
The Rudolph Rule
Rudolph the reindeer's red nose stood out from the other reindeers' and led them. Even small differences guide your audience to what's important. If you're presenting a piece of relevant data in a list, why not make the data of interest a different color from the list? Or circle it in red?
The Rule of Four
The brain can generally hold only four pieces of visual information simultaneously. Don't ever present more than four things at once.
The Birds of a Feather Rule
Organize information belonging to the same group by giving them similat visual tags -color or shape.
Jay, from Bangalore