Meta tags are used on websites as a source of information to help search engines decide on the order of listing and ranking of your website(s). Meta tags only provides metadata about the HTML document; typically used by search engines to specify page description, keywords, author, etc, and will not be displayed on your blog. Though not mandatory, meta tags should be implemented in the sense that it does impact your listing and ranking in search engines, thus the higher your page rank, the more traffic you can drive. All meta tags should be placed inside your head element.
Meta tags definition and usage
Your page title is the most important attribute for rankings. Your page title should be more than your actual page title and contain words located within the page contents.
*Blogger Blogspot handles the title for you.
Description Meta Tag
Description tags should contain a coherent description of your page, and should also contain words that are located within the page contents.
<meta content='Description Goes Here' name='description'/>Keywords Meta Tag
A list of keywords that describes your page. For better results, select between 10 to 15 of the most popular and relevant keywords to that particular page. Keywords can be words and/or paraphrases related to your page and should not contain more than 20, otherwise, search engines won't be able to detect the main theme of your page, thus watering your page relevancy down. The ordering of your keywords also impacts it's ranking or listing so use the most important first and least important last. To determine each keywords relevancy, use Google Analytics or Webmasters Tools.
<meta content='Keywords Goes Herename' name='keywords'/>Copyright Meta Tag
This tag simply indicates that your page and information is copy righted. For example, Copyright YOUR-BUSINESS - 2010.
<meta content='Copyright Company Goes Here - 2010' name='copyright'/>Author Meta Tag
This tag is used to indicate the name of the webmaster, blogger, or company.
<meta content='Author Goes Here' name='author'/>Email Meta Tag
This tag is used to display the relevant contact address for your page or blog.
<meta content='Email Goes Here' name='email'/>Character Set Meta Tag
This tag is used to let the browser know which character set to use for the particular page. Different character sets will render your page differently.
<meta content='text/html; charset=UTF-8' http-equiv='Content-Type'/>Rating Meta Tag
Rating meta tags enables search engines to set an audience content rating for your page.
<meta content='General' name='Rating'/>Robots Meta Tag
Robots are used to either allow or disallow index and/or crawl of a page.
<meta content='index,follow' name='Robots'/>Revisit Meta Tag
Because your page could be indexed and/or crawled several times a minute; the revisit meta tag will tell search engines when you want them to come back next after the first index/crawl.
<meta content='7 Days' name='Revisit-after'/>Expires Meta Tag
This tag is used to tell search engines when the page and it's content is no longer valid or available.
<meta content='Enter Date Here' name='expires'/>