On "show, don't tell", if it's not important, give it a quick description and move on. If it's vitally important, or the POV character happens to be paying very close attention for some reason, go ahead and stuff all the nuances you can into the description.
and it was wisely pointed out:
The failure mode of that is giving away what's going to be important later on and what isn't way too obviously early in the book.
I agree, that's an easy pitfall, which is one reason I think it works better as a style than as a tool, if you can get what I mean.
There are piles and piles of information that people are going to get from descriptions, they're not going to pay attention to all of it. Probably very little. So it's good to get those details out there, especially if they are allusions or foreshadowing. The trick is that you have to display them in the way that the character's going to notice them. Because the character's going to shrug them off now and later on that piece of the puzzle is gonna click into place in his head and you'll get that golden "oh shit" moment where time slows down and he catches what's wrong. You need to make the detail
sound neglible now and
be important later.
Take, for example, the mindfog in Summer Knight. At the time, Dresden just kind of acknowledged the fact that it was illegal sorcery, and started trying to deal with the situation. But those 2 words in themselves play a very important role in figuring out who his opponent is. He was facing a wizard, and one not sanctioned by the white council. Sure, faeries can do magic, but they tend to have very different methods and means by which they operate, so if it was faerie magic, he probably would have called it just that: Faerie Magic. He specifically said "illegal" though, which points to a form of magic which is moderated by a body of law. The white council is the only body of law that governs the use of magics. (The accords don't count. They help to round things out, but the accords are more of a treaty than a form of government itself) Given what he had to draw on so far from that book, the only wizard unsanctioned by the white council in the area was Elaine. So, we
could technically have parsed out from that point in the book that Elaine was playing both sides of the field, and this
does come into play later, when Dresden realizes he's been betrayed by her. He remembers the mindfog.
This is a very difficult technique to perfect. You want to get those details out there. You want the reader to acknowledge them. You want the character to acknowledge them. And you want them both to shrug it off for now. I suppose you could technically try making those details more obvious, but then your character has to be an idiot to not notice them, and the reader's not an idiot. He's gonna be sitting there screaming inside his head, "WHY ARE YOU IGNORING THAT YOU FOUND YOUR DEAD BUDDY'S DOGTAGS IN YOUR GIRLFRIEND'S PURSE!?!?!?! ARE YOU STUPID!?" So I suppose on this particular subject, we ought take Jim's advice: The reader's not an idiot. Get the information out there and let the reader find it. Your readers are always going to be smarter than you expect. They'll notice. (I don't remember where I saw him say that, but I am VERY sure I saw him say it... somewhere)