Mapping & Describing the dungeon

How do you describe the dungeon? What assumptions does that make about how adventurers progress through the dungeon?

I think when I learned to describe places, it was much like this:

"10', 20', 30', 40', 50', and the corridor ends in a T."
"We go left"
"10', and you find yourself in the middle of the west wall of a 30' x 30' room with a door opposite the way you came in."

Essentially:
- describe the area of the map you are in right now, with no assumption you can see much further than a few feet in front of you.
- assume you continue to move in the direction you said you'd go unless told otherwise.

In other words, you see the square you're in, and once you say "We go left" you keep going left until you say stop.

But I don't do that anymore.

What I do now is:

- describe what you can see from where you are right now.
- assume you aren't moving unless told otherwise.

My PCs generally have very bright light sources. A torch casts a flickering light over a relatively small area, but a bonfire-bright continual light spell throws a steady, even light out to 4 yards and gives you dimished vision out to 12 yards, according to DF2. So at the very least, I need to give some idea of what's out to 36' from the PCs.

Then you can couple that with the common access to Night Vision (reduces vision penalties, if there is any light) or Dark Vision (you can see in the dark, period) and I need to describe out from where people are. Characters with superior vision might see beyond that, or to the very edges of light with great clarity. In my GURPS game, I have a guy with Night Vision 6 and an 18 or less vision roll using a Continual Light stone. Compare that to a normal man with no Night Vision and a 10 or less vision roll and the same light source, and you can probably see why I assume the former can see very clearly on the fringes of the available light.

Not only that, I assume people are moving cautiously and are ready to stop at any time.

So what I do now is more like this:

"You see the corridor extends at least 40' into the darkness. It seems to continue past that."
"We move up the corridor."
"You move up about 10' and now your scout can see the corridor ends about 50' ahead in a T."
"We move up to the T and look left and right."
"To your left you see the corridor goes 10' feet and enters what appears to be a square room, 30' x 30', with a door opposite the way you came in, just on the edge of your light source. To your right [etc.]"

Big change.

I think that happened not only because I changed systems, but also because I spent so long running games outside of dungeons, with horizon-limited and terrain-limited LOS, flying characters, and so on. Not a lot of "you go 10' and it ends in a dead end" kind of stuff. So I lost that habit, perhaps, and pulled the feeling of "you can see far, and I'll assume you aren't moving until you say where to move" play from there to my dungeoneering.

Not only that, but I got used to parties moving in "patrol" fashion instead of "ranked formation" fashion. We don't have 6 characters marching 3 across and 2 deep like in an old-style video game (or like the example party in the AD&D Dungeonmasters Guide.) We tend to have one in the lead, one or two behind, and then a trail of PCs in pairs or singly, with a clear rear guard trailing at a short distance to deal with threats from behind. So I can't even assume they all singly move together as a unit - or that once they turn a corner what's ahead is in view to all and what's behind is lost to everyone.

So my mapping description has changed a lot, even if I didn't describe distances vaguely ("about 30'" or "roughly rectangular, maybe 100' by half that.") and directions relatively (left, right instead of north, south)

How do you do it, and has your style changed over the years? Is there anything you do that seems to work extremely well in getting the description across, keeping things moving, and yet doesn't needlessly confuse or make assumptions for the players?