The most common presentation mistake is treating slides as a script -- packing them with full sentences and then reading them aloud, which causes the audience to either read ahead and stop listening, or disengage because the speaker has become a narrator for their own slides. The 'one idea per slide' principle keeps each slide focused on a single point, using a short headline, a key number, or one supporting image rather than paragraphs of text, which keeps the audience's attention on the speaker as the primary source of information. A well-known (though informal) guideline is the 6x6 rule: no more than six bullet points per slide, and no more than six words per bullet, as a ceiling to prevent text overload -- in practice, even fewer words per slide is often stronger. Visuals (a relevant chart, photo, or simple diagram) communicate faster than text and are processed by the brain more quickly, so replacing a paragraph of text with a single clear chart or image usually strengthens, rather than weakens, audience comprehension.