The organization of slides should be hierarchical. By only reading the titles on each slide, the reader should capture the whole story.
Use as many pictures, animations, videos as possible. These are called hooks, which are more enticing than text and formulas.
Do not stuff too many words, or even worse, too many formulas on each slide. One point per slide and one slide per point.
Unify the font, color, etc. At most three different colors (e.g., pure blue, pure red, pure black), one font type (e.g., Times New Roman (good for PDF), Arial) and three different font sizes (e.g., 32, 24, 18) to distinguish title, subtitle, and context.
For non-professional readers, use as few jargons as possible. Make sure each jargon should be used before well defined. Try to replace jargons with plain words.