Making beautiful slides helps, but there is no magic bullet here – not everyone is a professional graphic designer (this handy “guide to visual design for everyone” can help though). Keep these points in mind to avoid the most common mistakes:
• Use animations sparingly. They are most useful when used to focus and direct the audience’s attention. The best way to do this is to use the “appear” and “disappear” animation: start a slide with a single sentence or image, and then add to it using the “appear” animation.
• Have a cohesive color scheme and design. All slides should feel like they’re part of the same presentation, not just a random mix of styles and themes. For inspiration, see this website’s most popular palettes.
• Use large photos as backgrounds if possible. Search on Flickr or Google Images for photographs shared under a ‘Creative Commons’ type license. For more on this point, see this fun, excellent tutorial for details, and this one.
• Avoid 1980′s-era clipart. Use large, beautiful photos instead; see point above.
• Limit your text per slide to 1-2 short paragraphs, at most. Better yet, keep it to a few, simple sentences. Leave the details for your publications, and refer your audience to those publications if you wish. This also helps keep your font size large and legible, a very important consideration.