Be careful not to step on each others' feet. Hold on to a strap if you can. Don't push people with your hand or elbow - If you do that, you will without doubt become involved in some trouble. Though the commuters look calm, most are frustrated deep inside. Women should be careful, because there may be a man who touches them up in a crowded train.
Some Masters say that they can even sleep in the crowd, once they get used to it.