What I do to avoid being sanctioned when I'm explaining rules:
Don't even say the word sanction, unless it's dire circumstances and they're being decidedly non-chalant (in which case, you politely and nicely say that breaking rules can be sanctionable).
Don't be angry. Just don't. If you're in an angry mood, why are you even on Disco? If you're angry after being blown up unfairly, walk away.
Throw in some smiling faces (with //s before everything of course, to show you're not trying to be threatening. Don't just throw smiles on it unless you're sincere; it'll show.
Put yourself in their shoes, and try to imagine how they might feel.
Don't assume their English is weak, but if it is, try to simplify your language usage.
Don't just quote rules. First and foremost, direct them to the forums. Politely.
Don't even mention it if you're unsure if they broke the rules. If you're in this situation, you can read the rules at discoverygc.com:)
If you broke the rules (even a little) or went against 0.0, apologise. Sincerely. And maturely.
Obviously what's sanctionable as 3.4 and not has been clarified, just thought I'd add my list of things:P
EDIT: And report where appropriate. You're only explaining rules if they don't know them.