1. Description_ Meta tag:
Meta tags are becoming less important but there are meta tags that still matter, these are the <description> and <keywords> ones. Use the <Description> Meta tag to write the description of your site. Besides the fact that Meta tags still rock on Bing and Yahoo!, the <Description> Meta tag has one more advantage – it sometimes pops in the description of your site in search results.
2. Keywords_ Meta tag:
The <Keywords> Meta tag also matters, though as all Meta tags it gets almost no attention from Google and some attention from Bing and Yahoo! Keep the Meta tag reasonably long – 10 to 20 keywords at most. Don’t stuff the <Keywords> tag with keywords that you don’t have on the page, this is bad for your rankings.
3. Language_ Meta tag:
If your site is language-specific, don’t leave this tag empty. Search engines have more sophisticated ways of determining the language of a page than relying on the <language>meta tag but they still consider it.
4. Refresh_ Meta tag:
The <Refresh> Meta tag is one way to redirect visitors from your site to another. Only does it if you have recently migrated your site to a new domain and you need to temporarily redirect visitors. When used for a long time, the <refresh> Meta tag is regarded as unethical practice and this can hurt your ratings. In any case, redirecting through 301 is much better.