When exiting the Metro from an underground station that you've never been to before, it can be difficult to determine which way you are facing when you make it up to street level. It would be helpful if Metro would put some signage by each escalator bank out of an underground station to tell you which side of the street you are on, and perhaps put a compass rose decal on the floor to tell you which way is North.
I've found similar signs in the NYC Subway system to be extremely helpful; if an exit is under an intersection, for example, different signs out of a particular station may indicate whether you're walking out at the "NE Corner" or "SE Corner". It wouldn't be as simple as that for many WMATA stations, but a good example would be to tell the riders "West side of Connecticut Ave" when getting off at the Woodley Park station. Displaying the cardinal directions with a big compass rose decal on the floor before heading up the escalator banks would also help riders to get oriented when coming out from underground.