OK - Google doesn't actually tell you this (although they drop a lot of hints).
But good SEOs (and there aren't many of them) do research on this as part of their job.
It comes down to a whole series of factors:
- encryption - encrypted sites are safer than non-encrypted sites and so rank higher.
- speed - people prefer faster sites, so they rank higher.
- mobile friendly - most website access is on a phone, so sites that work well on a small screen rank higher.
- structured content - people don't just access information in a browser, voice assistants and other technologies are gaining in importance, so structuring your information so that they can understand it too is vital
- optimised images - descriptive file names, compression, captions all help screen readers and other technologies.
- domain age - if your domain is brand new, there's more chance that your some sneaky spammer site, if your domain is really old, then you're probably an established quality business.
- authoritative backlinks - getting links from other sites is still important - but you only want quality links. Getting links from thousands of shady SEO spamblogs is bad, getting links from the number one journal in your industry is fantastic.
- quality - this is the most important factor of all. The stuff on your website has to be of high quality. It has to have authority. You have to appear as an expert in your field. If you do, then people will want to access your stuff. If people want to access your stuff, Google will want to show it to them. So hire an amazing photographer, a great videographer, an outstanding copywriter (the most important of the lot), because those things are what makes all the difference.
Take action: Add some quality to your website.