I've worked with kids for years,
and there's no denying that simple works best.
That's why I always say that I only have two rules:
1) Be Nice.
(TDDP #7 "Be Nice" $25)
This is pretty much an all encompassing rule.
It sums up no hitting, no stealing, no yelling, and a boatload of others, because all I have to say is,
"Do you think that is being nice?"
(the answer is usually no, but regardless, it gets them thinking about how they're acting)
I absolutely enforce rule number one, and I wish I could pass it along to some grown ups, because it is tantamount to being a decent human being.
Not tipping your server?
Attacking someone publicly, instead of talking to them privately, on Facebook?
Taking up two parking spaces?
Talking behind someone's back?
Do you think that is being nice?
My second rule is "You make a mess, you clean it up".
Unfortunately, I'm usually the one who makes the messes, so this one comes back on me a lot.