It is always a good idea to set your SEO keywords, descriptions, and page titles. These are key terms that search engines use to rank and find your site. In the Website Builder, there are two places to set SEO keywords: Page Settings and Site Settings. These are for page specific SEO terms and global site SEO terms, respectively. Here is an example of how to set keywords, descriptions, and titles for your site.
Keywords are the terms that people search for while trying to find your site. The important part about keywords is that they match the content on the desktop site. Meaning that if you are running an oil change station, you should not have keywords relating to sushi. Here are the Keywords that CNN.com uses:
CNN,CNN news,CNN.com,CNN TV,news,news online,breaking news,U.S. news,world news,weather,business,CNN money,sports,politics,law,technology, entertainment,education,travel,health,special reports,autos,developing story,news video,CNN Intl
Notice that the keywords relate exactly to what CNN does. Also, they do not repeat CNN in every single keyword. CNN could have easily put CNN news travel, CNN news autos, and so on, but they know that repeating keywords is not a best practice.
The description is what shows below your title on search engines. A good description is between 130 and 170 characters and tells an accurate description of what the site is about. Here is an example description for a mobile website builder:
The fastest, easiest way to build a great looking mobile website in minutes. Includes hosting, site analytics, click-to-call, mobile maps and more
This description is 146 characters and accurately describes what the service does.
The title tells users and search engines what the page is about. Make sure titles are clear about what users should see on the page. This is one of the most important steps, as the title of the page is directly what shows up in search results on search engines. Also make sure not to repeat keywords in titles, as this can be seen as trying to spoof results.
If you want to learn more about SEO best practices:
Getting started guide released by Google (only available in English)