Bring two shirts: one white tee shirt and a dark shirt. (Not just a non-white shirt.) You will want change your shirt to join the side the organizer says you should go onto, but it is also ok to just join the side with the fewer players without asking.
If you see someone, don't be shy to ask if they are there for the game. If it is your first time, try bringing a soccer ball since that is the universal language you are down to play any soccer pickup.
If you are using the meetup app you may need to click here in a browser: (http://www.meetup.com/dcsoccer/photos/1068687/#[masked])
This picture shows 9 grassy fields between 12th St., 14th St., Madison St., and Jefferson St. We meet in the exact middle of the middle grassy field closest 12th.
Metro walking directions: Smithsonian metro stop. Walk due north-west.
Parking: unlike the Ellipse, there is a lot of parking near the south side of the mall.