Our current /help/on-topic page is just the default boilerplate, and doesn't really help new users learn what kind of questions are on-topic here. It's definitely in need of improvement.
What topics should the Help Center cover? I have posted a single Community Wiki answer containing our current /help/on-topic page (that you should feel free to edit and improve), but you can also post answers of your own if you have ideas for what the page should contain but don't want to actually write them.