The best approach I've found is (at first) to do nothing… not until you establish pattern of problems that regularly show up in actual practice. You may want to fill in a line or two that describes your subject space, but let the participants use the site intuitively before you start enumerating a lot of rule discussions with rare (and often hypothetical) problems that haven't actually come up much in actual practice.
When it comes time to elaborate on your scope, here is my preferred format (adapted from the Help Center at Superuser):
What topics can I ask about here?
Computer Science Educators is for <brief elevator pitch>. If you have a question about …
- <try to cap it at three summary points>
and it is not about
- <if you need more than three common prohibitions, you're probably doing it wrong>
… then you're in the right place!
Please look around to see if your question has been asked before. For more help, see "What types of questions should I avoid asking?"
If your question is not specifically on-topic for Computer Science Educators, it may be on topic on one of our related sites:
- <list of related sites with "when it's better to ask there" pointers>
And if your question is about the site itself, you can ask on our Meta Support site.
A Note of Caution
Please resist the urge to use the Help Center as a community-pet-peeves dump by enumerating every way you can possibly suck at Stack Exchange. Some sites have a bad habit of loading up a growing manifesto that looks more like "If I only knew these 57 things before I started…" — but they usually end up making the site look more unapproachable than helpful.