By revealing one point at a time, you guide your audience's attention and simplify how they process your message.
You can present a complex diagram as long as you highlight the portion you're discussing.
Too often we shoehorn too much information into one slide. Then the message gets camouflaged in noise or clutter.
Slides are a visual medium. They are not
good substitutes for books or handouts. Balance your text and graphics
to best get your message across. Only include headings as high points
so you can present the details. And for heaven's sake, don't read your
slide to your audience! They can read for themselves.