When preparing a presentation, it's tempting to fill your slides with as much content as possible. But it's your job to carefully arrange the elements so that your audience can both process the information and hear what you're saying. Don't crowd the slide with so much content that it competes for attention. Respect the white space (the open space surrounding items of interest). Provide a healthy amount of it and you'll impart a feeling of luxury — advertisers have discovered that it creates higher perceived value. That doesn't necessarily mean that everything is literally "white," just that the design feels spacious.
Source: Today's Management Tip was adapted from the HBR Guide to Persuasive Presentations.