The most important thing is to wear appropriate footwear when walking on the train - especially between cars! Getting your toes caught between the plates is no picnic!
The Traveler makes a great point here. Proper footwear is important for several reasons, including potential injuries when crossing car couplings
and in consideration of the unknown cleanliness of the floors. Keep in mind that while the floor may
look clean it may be far dirtier than you first realize. Different passengers will have vastly different levels of hygiene and bathroom etiquette and even hallway floors may have been contaminated with untreated human sewage after toilet system failures. Trust me on this; I've seen it happen. Wearing proper footwear is one of the few things I've seen OBS make a big deal about and it's definitely worth the effort to put your shoes on whenever you're up and about.