If you have the opportunity to describe something, give it one to three short, succinct details that make it stand out. Use the technique for characters, locations, objects, or anything else that you want to introduce into the narrative fiction that you and your friends are creating.
I’ll point out, as Rob D does in the comments to that post, that Roger Zelazny’s been quoted a couple times as ascribing to this method of conveying character in his books, and Zelazny does nothing better than introducing characters in one or two sentences that jump off the page and slap you in the face so you remember them.
Hell, this isn’t good advice for gaming, this is good advice for creation of story in general — while I’m tweaking up Hidden Things with some recent input, I think I might boil down some of the characters when they’re introduced and see what happens. A little voice in my head is telling me that most of my characters are introduced with about three details already. I hope that’s true.
I overdetailed Rowena Gower in my Galactic game yesterday… not a lot, but a bit. (Not counting all the ecological evangelizing she did, just facts about her.) Hmm.
Anyway. Really really good rule.