What do you really want from your slides? You want them to improve your communication—make it clearer and more concise. Also, you want to produce an emotional impact. Coincidently, this is precisely what the audience wants. They don't want decoration. They want clarity, and they want to be alive during the process. So design is not about decoration; it's not about adding stuff. Rather, it's about following simple rules and ruthlessly deleting everything that doesn't fit.
SLIDE DESIGN—THE MINIMALIST APPROACH
There's a very effective solution to “the zoo” problem I mentioned earlier with presenters using a million fonts, colors, and styles of pictures: just use white background with black Arial font, a minimum amount of illustrations, and no other colors for your diagrams. This gives the slides a very strict look and produces a much-desired uniformity. By the way, if you don't want to know anything about design, it's best to stick to this approach. It works. It is certainly not the best approach, but it clearly says that you are concerned with substance. Some people appreciate that.
However, beautiful as it is, this approach fails on one important count—it doesn't invoke emotions. It doesn't take advantage of the aesthetics-usability effect. It misses the opportunity to differentiate ...