I was in a rush when I wrote my other post. I have a few more things.
Never appear surprised or shocked by anything you see (even if you are). As a corollary, Don’t stare at people on the subway or anywhere else, no matter how freaky they are. Read a book or space out into the middle distance. (Long subway trips are good for achieving a Zen state of No Thinking)
The unwritten rules of subway riding indicate that you should never sit directly next to anyone when you have the option of sitting one seat away. Obviously if you do not have this option you should sit in any available seats. For example, in a “3-seat” configuration, O representing an empty seat, if you see someone sitting XOO, you want to sit XOX, never XXO (unless you know each other, and even then). the next person to come along would be justified in sitting in the middle, if no other non-adjacent seats are available.
On a more serious note, if you are on a crowded subway and someone is trying to touch you inappropriately (it happens) say in a LOUD voice, something like “Some Fucking Loser is Trying to Grope Me.” The groper will usually be intimidated by your outspokenness, and very often other passengers will come to your aid. Marines on shore leave and large Jamaican ladies are good for putting a beat down on pervs.
Don’t make eye contact with anyone you don’t want to speak with. Simply ignore anyone skeevy trying to get your attention. Just because someone talks to you, doesn’t mean you’re required to talk to them.
Help people who seem more confused than you. Especialy tourists on the subway. If you realize some tourist is blatantly making some huge error (going uptown when they want downtown, using an old subway map that isn’t accurate, etc.), just butt right in and tell them. Being right and butting in are New Yorker attributes.
Subway maps are free at any kiosk. Get one and take it home. Study it there. Do NOT, EVER open up a subway map or map of any kind in front of other New Yorkers… have you no pride!? If you need to double check yourself, casually check out the large map posted on every platform and in every car near the door. Every station has local neighborhood maps near the exits as well.