Unfortunately if you find yourself needing to bring luggage onto the metro, there are no overhead bins or conveyor belts that carry it away to be checked. So what can you do?
Generally blocking the path for others to exit or enter the train is an unpopular idea, so try to not use your luggage for crowd control. When you're ready to get on the train, aim for one of the two end doors of any car since there is usually more room for maneuvering there. The middle doors can be a hotbed for crowds and discomfort. If the car isn't completely packed, try to grab a spot along a wall, helping keep you and your bag out of the commuter escape route. If you find yourself in the aisle, be ready to shuffle around when someone needs to get up from a seat.
If you're lucky enough to actually snag an aisle seat, you can keep your bag next to you without it taking up the entire aisle. Some bags can even fit under seats, though the least awkward place for this would be the more open seats near the door. You may even find yourself and your luggage on a pretty empty train (yes, there is a short period of the day not deemed rush hour) with your choice of seats. If that happens head to one of the seats near the door where you can keep your bag in front of you, making sure it doesn't fall down and simultaneously keeping it out of the way.
Through all this try not to run over anyone's toes, get your bag caught in the train doors, forget your bag on the train, get caught in a turnstile, or let the bag knock over a small child.
Or share your own luggage suggestions below.