You can at anytime claim seniority and get a seat, if you have been on the train longer than someone who is sitting.
Leaning on the doors is totally fine.
If there are multiple seats available, always sit in the one with the greatest number of surrounding empty seats, unless one is between two pretty girls.
If the train is squeezed so full that you are touching the people around you, you must avoid eye contact at all costs.
You can sing along with your music as long as its not Justin Beiber.
All service changes, even planned ones, suck.