SEO is a massive topic and what you need to do really depends on your site, so it's not really something people can just say "do this!", you'll have to do your own research. But here are some general pointers:
- A well configured server that uses standard protocols like HTTPS
- A well structured page (headings and img alt tags are used correctly)
- A fast page on both desktop and mobile
- Good, relevant and keyword heavy content
- Backlinks with good keywords on sites with good domain authority
- Using noindex/nofollow tags on irrelevant content
- Blocking google from accessing irrelevant content through your robots.txt
- Using something like Cloudflare as a CDN (also works as DDOS protection too!)
For Cloudflare, there's a couple other things you can do with it like minify your HTML/CSS/JS so that whitespaces & newlines are removed.
SEO is also a very long process and you will not see results from anything overnight - it generally takes between 1-3 months for changes to take affect. I've only started adhering to all of the above pointers in the last few months, but I am definitely starting to see an improvement.