First, no golden rule, use what's working for you
The main reasoning of not miking directly the soundhole is that there you pick all the strumming (and a boomy sound), which is not what someone is hearing say, 2 or 5 meters from the guitar. But you can't mike an acoustic guitar that far, it sounds dead.
Well, I should have wrote: between the octave and the end of the neck. If you use only one mike, I don't mean pointing directly toward there, but rather: point to the soundhole, then shift the mike toward the neck.
Miking there gives you more presence, and it's the spot where you're supposed to have the more defined sound.
If you prefer a sound more soft and "fuzzy", the other spot is near the bridge, under the right hand, or slightly right of it. That's why I usually use two mikes, to try and find a balance between these two sounds.
I've found an article on stereo miking:
http://www.humbuckermusic.com/acguitrectec.html. You'll see there they are miking nearly exactly on the octave.
I've another interesting article backing exactly my point. Excerpt:
"Recording acoustic guitar is a challenge, to be sure. The sound hole can really put out some lows that can be uneven when compared to a live in-person experience.
Having the mic back is fine, although at 3 feet you're getting room sound as well, and a less immediate version of the guitar. If the room acoustics are good, that's ok. Try a foot instead, aimed between the soundhole and the end of the guitar where the neck is joined. If you want more lows, just twist the mic more toward the sound hole (or don't twist it and just add some eq)."
The full article is at http://www.johnvestman.com/ac_guit.htm
As for the distance (between the mikes and the guitar), the best advice I've seen is "two hands".