This is a basic idea. The site must be found on search engines, meet accessibility standards and provide great user experience.
This begins with keyword research-- knowing what users type into search engines when they want to find the website. This also includes SEO strategy and measurement. Tracking the number of inbound links plus gaining new ones. Checking to make sure all the pages are indexed on search engines.
Finally, adding new content to continue to grow user experience and inbound links.