Can Google actually crawl your site?
Check robots.txt for a blanket Disallow and check your pages for a stray noindex tag. Nothing else on this list matters until both are clean.
Visit yoursite.com/robots.txt in a browser. If you see Disallow: / under User-agent: *, your entire site is asking search engines to stay out. This happens most often when a staging site goes live without the developer changing the file back.
Then view the page source of your homepage and search for 'noindex'. A single leftover tag from a redesign can remove a page from Google entirely while the page looks perfectly normal to you.