This thing is a mysterious black box. I'm going to unravel it. Go to Google Search Console.
This is Google's own tool for submitting your website to Google's index. If you haven't submitted your site to it, do it next. Go to search results, toggle on average position.
Look for keywords between positions 6 and 11. These are ranking either the bottom of Google's first page or the top of its second. Click a keyword that looks interesting.
See the page that is ranking for it. All you have to do to improve your ranking for this keyword is add a few extra sentences to your page about it. I did this recently and went from position 10 to position 1 for a keyword.
I hadn't been using the exact keyword, so I just added it to the page's introduction. That was enough to go to position 1. SEO does not have to be hard, but for so many people.