Extend your website continuously with new and up-to-date content. This way:

• You offer visitors and potential customers new up-to-date information.
• Search engines will crawl your website more often and rank the new content higher (the first page in the SERPs usually has popular and up-to-date websites on it).

After you updated a page, don’t forget to update the XML sitemap as well. You can do this by defining the last modified date in the link properties of the Site Map Generator.

Google Blog: Giving you fresher, more recent search results