Waiting on the platform for the next sardine express to arrive is the ideal time to get warmed up. A couple of neck twirls, hip twists and ankle rolls are a good way to get your body limber for the ensuing battle. The platform is probably more neglected than it should be. Good platform position ensures a nice entry onto the train and the potential to grab some prime real-estate before the next guy does. Ideally you should be positioned closest to the opening door, just aside to allow disembarking passengers to spill out, but not too far to the side lest passengers pushed out who intend to re-board get the jump on you. On a super crowded train (and what else is there during Tokyo rush hour) the possibility of getting a seat is nil. Seated people typically board the train at its point of origination, which is evidently somewhere north of Russia. These people guard their seats with the territoriality of a pit bull. Most likely they have strapped on pampers to prevent bodily functions from forcing them off their foot squared perch. So let's put the idea of competing for a seat to rest. Still there is certainly a pecking order among the standing. The best standing positions are halfway between the doors, directly in front of the seats. This position is as far away from the door areas as possible translating into the minimal possible squeeze. Also this position gives the passenger access to the overhead rack. Being a good salary(wo)man, you will undoubtedly have a briefcase of sorts that will strain your shoulder over the course of time so the overhead rack is a luxury that shouldn't be understated.
The second best position would be standing immediately behind position number one. This position eliminates some squeeze, but does not give access to the overhead rack. Now, the worst possible position is debatable. It is either directly in front of the door - photos of gloved train station attendants pushing people come to mind - or in the center of the door area. Either way your crushed. Is it better to be crushed between two human bodies or simply a human body and door? I leave this point unresolved and would encourage the reader to experiment with both (as a commuter you would undoubtedly have ample opportunity to do so) before choosing which constitutes the greater hell. When arriving a train station that you do not intend to get off at it is important to jockey for more prominent positions in the pecking order. This often runs contrary to common sense and decency on public transportation. Unless you are pancaked against the door, under no circumstances get off the train. If you do get off the train you are right back on the bottom rung and the cycle becomes endless. The thing to do is A) guard your position if it is good or there is no possibility of improvement; B) push your way inward toward a more prominent position that is opening up. The reason this flies in the face of common decency is that at the very least you will be hindering someone trying to get off if not pushing directly against them. Alas, this is the country that gave birth to Sumo. If you are trying to de-board you can use your bag as a sort of shield to push through the crowd. As a foreigner you will likely have a height/weight advantage. Don't be afraid to use this; there are no rules - it's war!
I hope that this quick tutorial will give you sporting chance should you step on a Tokyo rush hour train, but practice makes perfect so if you really want to get good you'll just have join the suffering masses and battle it out on a daily basis.