For effective presentation slides, you should apply the 6 - x - 6 rule to most slides. The 6 - x - 6 rule means

For effective presentation slides, you should apply the $6-$x$-6$ rule to most slides. The $6-$x$-6$ rule means that

 a$.$ each slide has no more than six words per line and no more than six lines.

b$.$ each slide is discussed for six minutes.

c$.$ each main idea has no more than six bullet points.

d$.$ the entire presentation has no more than six slides.