When Google is considering a page, it needs to be able to figure out what the page is about, and it uses those elements as clues to whether or not a page will answer a user's queries (based on the Keywords they used.)
- Questions asked by Google when they consider changes to their search algorithm (what they use to rank results)
Page Elements
When Google indexes a page, it considers all the content on the page when trying to determine what the page is 'about'. It especially gives priority to:
- page title
- url
- heading tags
- sometimes: meta tags
If you want your page to do well for specific Keywords, make sure they appear in the above elements.
Page Content
Search engines also require enough content text to determine the page's topic: aim for at least a moderate paragraph (approximately 3 sentences). This allows Google to make sure that the result will be on-topic with the user's query. Remember, Google wants to provide the best search results (ie. results that match the query as closely as possible) for their users.
From Google: “Our advice for publishers continues to be to focus on delivering the best possible user experience on your websites and not to focus too much on what they think are Google’s current ranking algorithms or signals.”
Also keep in mind that items in tabs may not appear in search results because the content doesn’t display when a page loads and is therefore harder for visitors to find. Google wants to send its users as directly to content as possible, which means that content needs to be immediately available as possible when landing on a page.
See also: Google's Search Engine Optimization Starter Guide (pdf)