While it is possible to overload your audience with too many visuals, the more typical problem is too few visuals. Allow approximately one minute per visual. Slides and overheads should make an impact quickly and then move on. If you have a complicated concept to communicate, start with the ground level and use three or four slides to complete the picture. Be careful with color.
Color can add interest.
It can also detract if used haphazardly without planning. Plan your color scheme and use it faithfully throughout. Make your visuals easy to read. Use large, legible typefaces. You can effectively use up to three different sizes of type, but use only one or two typefaces.