Meta Description and Keywords Tags
Meta tags have become devalued by search engines in the past few years, due primarily to the fact that they were abused by spammers. However, some search engines still lend them some weight, so it is important to include them nonetheless. At the very least, you should both description and keywords tags on each page.
The description meta tag should provide a brief synopsis of the page. This text can occassionally show up underneath your site’s title in the SERPs, so be sure to compose it for maximum clickthrough. You will also want to include as many of your key phrases as possible while maintaining good readability. Lastly, be sure to keep the character count of your description under 150 characters or so.
The keywords meta tag should include your most important key phrases. Use commas without spaces to separate each key term, do not repeat any particular word more than three times, and keep the total character length at or under 200 characters. Follow these steps and you can rest easy knowing that, at least with regards to your meta tags, search engines will look favorably (or at least without disfavor) on your pages.