PowerPoint uses slides with a horizontal or “Landscape” orientation. The software was designed as a convenient way to display graphical information that would support the speaker and supplement the presentation. The slides themselves were never meant to be the “star of the show” (the star, of course, is your audience). People came to hear you and be moved or informed (or both) by you and your message. Don’t let your message and your ability to tell a story get derailed by slides that are unnecessarily complicated, busy, or full of what Edward Tufte calls “chart junk.” Nothing in your slide should be superfluous, ever.
By Garr Reynolds: http://www.garrreynolds.com/preso-tips/design