I was born in the Dark City, so our ways have always seemed ordinary enough to me, but I can also understand that a visitor may need some help getting used to us. Thus, I’m writing both to welcome you and to pass on a few words of advice.
The first thing you need to remember is that morning coffee is usually brewed with water from the River Styx. Having drunk it, all oaths you make until it’s passed through your system are absolutely binding. The gods themselves cannot break an oath made by the Styx, so be very, very careful with your language while here. In particular, I urge you to avoid the construction “I’ll be damned if I [go to the Opera/ write my Aunt Petrohilos/ change my socks}.” When, as is inevitable, you go to the opera (possibly with your Aunt Petrohilos, and wearing a pair of clean socks), you will, of a surety, be damned, and your friends will have to mount a costly and dangerous expedition to extract you.
That is, we’ll mount such an expedition if we remember who you are. Another thing to keep track of is that bottled water in the DC comes from Lethe. (A small glass before retiring guarantees peaceful dreams. However, too large a glass guarantees not only a restful night but some time without a clue as to your own identity. I once experienced this, and was persuaded by my brother when I awoke that I was a blind street musician named Snigg. I spent a month tapping my way around town, building up quite a following for my virtuoso therebo playing. It wasn’t until a particularly hot day that I suddenly, in mid-madrigal, recalled that, while I couldn’t play a note, I had keen eyesight. Since you’ll be staying with us, I should warn you that my brother, the Marquis, still has the therebo somewhere. You can tell him from me by the squint, unless someone is shining a bright light into my eyes at the moment).
There’s no point in warning you to avoid the ambrosia, which vaguely man-like creatures roll into town in barrels now and again. Simply get drunk on it, as everyone else does, and you’ll pass for a native.
Its probably best to eschew religious conversations, as serious theologians tend to carry small arms when they socialize. If you must speak of things ecclesiastic, remember it is a matter of historical record that God has frequently manifested Himself (or Herself, if you live south of Weary Street) in the Dark City, almost always as a cat. The prudent, accordingly, treat all cats as if they may be God. Do not goggle, then, when someone mentions that they saw God chasing a mouse through the Drachenfells, or that God hissed at them when they stepped on His tail. (As I write you, God is sitting on a windowsill next to me, staring at a dust mote).
If you walk in the park, remember that the trees know martial arts and that the squirrels are prone to bitter sarcasm.