The first rule for website accessibility

ditch the mouse, test with your keyboard

There are a zillion rules for making sure your website is inclusive. There are checklists all over the web. I think the first and most crucial test for ensuring accessibility is to navigate your website with just the keyboard.

No mouse, no trackpad, or touch screen. Just you and the keyboard. That is it. Make sure you can ditch the mouse before you even try an automated test.