Headroom is GOOD room. Work *where the gear is designed to work* and you can't go wrong.
Tracking - Individual tracks should have the "meat" of the signal at 0dBVU. Depending on the preamp, that'll be somewhere between -22 and -18dBFS or so, with occasional peaks slightly higher. Fast transients (snare, etc.), keep a little more room in there and look for peaks no higher than around -12dBFS or so.
This is how the system was designed to work, this is how it's done "downtown," ideal signal, best clarity, best focus, ideal S/N ratio, etc., yada, yada, yada.
If you track properly, the mix should almost take care of itself as far as levels are concerned - Most faders right at unity, you can expect a mix to not need the attenuation that a "hot-tracked" mix would need. A double positive - Easier to mix - Better sounds to mix from.
I disagree with staring to a point also - Mastering shouldn't be "shooting for" anything except the best sound. 10+ years ago, I really didn't even pay attention to the final level. If it was -2 or -0.2dBFS, it's not like I was going to normalize it to gain something that no one was going to notice. It wasn't worth it. But by "today's" standards, I suppose and admit that most projects coming out of here are whacking -0.5dBFS regularly.
Either way - Keeping that headroom at every stage of the game is *so* dreadfully important, I can't even imagine where the "get your levels as hot as you can" train of thought came from (obviously not from listening to the results).
Most people are going to use up all of their headroom during mastering anyway - Use it up ONCE - Not at every chance you get. Your mixes will be more dynamic, more punchy, more open, LOUDER in almost all cases - There is no down side. Nothing to lose, everything to gain.
