The quality of the MC (main content) is one of the most important criteria in Page Quality rating, and displays the Expertise, Authoritativeness, and Trustworthiness (E-A-T) of the page. For all types of webpages, creating high quality MC takes a significant amount of at least one of the following: time, effort, expertise, and talent/skill.
I started by replacing all my low quality iffy main content with good quality. Especially on YMYL pages. Bite the bullet and hired a decent writer. Pages that I could not come up with content for I excluded from my sitemap until I could get content. Google can tell how much effort it takes to build, maintain, and improve your website. The effort you put in is a ranking factor.
After I had a content strategy I focused on monetization- I took ads off pages, changed location of ads, titled ads and reviewed ad locations that did not get clicks and just removed them.
Thirdly I focused on site performance and still working on that currently with the help of lightspeed, google page speed, and gtmetrix.
I used to chirp in the forums and complain about google, the guessing game, the zombies etc etc but they aren't changing and I'm not about to get a new career(yet). Unfortunately, John Mueller isn't going to audit my website after each and every algorithm update. The search quality guidelines is the closest I'm going to get to that. There are lots of little nuggets in there that you can find on your own.
Oh and also.. I compared my websites to my competitors with a fine tooth comb. See if you can find some weaknesses and make sure you are strong in their areas of weakness. If you have the time and resources launch more websites in the same niche with a different angle. As many as possible. Use those websites to test different strategies to see what google likes best. Then rinse and repeat. Long grueling process but it's the only way I made this business work for me.