, would be enough for a whole article, one that I’m not sure I’d be qualified to write. A few examples would be:
Making sure your site has a skip-to tab link, if needed.
Calling elements what they are on a page. If it is a button it needs to be a button tag (NOT a div). If it is a list it needs to be a list tag, etc.
Being careful about Aria attributes and not abusing them, they can be very tricky and can severly hinder a site if used incorrectly.
Following the W3 web standards (not w3 schools!) and guidelines for elements you’re using on your page.
Making sure your page can still function properly without styles and JS.
Making sure your scripts handle what they need to in the script, not heavily relying on attribute event handlers or hidden elements.
Keeping in mind browser support. (https://caniuse.com
is a great site for this) There are a lot of users using older technology, it is important to make sure your site will work across different browsers and devices.
There’s of course a lot more on this, but these are just some examples of the things I know our team considers when putting things out there in the real world.