Accurately summarize the page's content - Write a description that would both inform and interest users if they saw your description meta tag as a snippet in a search result.
• writing a description meta tag that has no relation to the content on the page
• using generic descriptions like "This is a webpage" or "Page about baseball cards"
• filling the description with only keywords
• copy and pasting the entire content of the document into the description meta tag.
Use unique descriptions for each page - Having a different description meta tag for each page helps both users and Google, especially in searches where users may bring up multiple pages on your domain (e.g. searches using the site: operator). If your site has thousands or even millions of pages, hand-crafting description meta tags probably isn't feasible. In this case, you could automatically generate description meta tags based on each page's content.
• using a single description meta tag across all of your site's pages or a large group of pages