DO
Accurately summarize the page content
Write a description that would both inform and interest users if they saw your meta description tag as a snippet in a search result. While there's no minimal or maximal length for the text in a description meta tag, we recommend making sure that it's long enough to be fully shown in Search (note that users may see different sized snippets depending on how and where they search), and contains all the relevant information users would need to determine whether the page will be useful and relevant to them.
Use unique descriptions for each page
Having a different meta description tag for each page helps both users and Google, especially in searches where users may bring up multiple pages on your domain (for example, searches using the site: operator). If your site has thousands or even millions of pages, hand-crafting meta description tags probably isn't feasible. In this case, you could automatically generate meta description tags based on each page's content.
Imagine you're writing an outline
Similar to writing an outline for a large paper, put some thought into what the main points and sub-points of the content on the page will be and decide where to use heading tags appropriately.
Use headings sparingly across the page
Use heading tags where it makes sense. Too many heading tags on a page can make it hard for users to scan the content and determine where one topic ends and another begins.