A good general rule of thumb for photography in DC:
“Get Closer”
It appears to be an almost universal impulse for tourists to stop when they see a famous building in DC, and take a picture or have their picture taken in front of it. And by in front of it, I mean 5 blocks away. So many people stop halfway down the mall, to take pictures of the Capitol building.
Stop it.
Get closer.
On an average camera with an average lens, you can literally be on the grass in front of the capitol before you fill the frame. And no one is going to be impressed by a photo of the White House taken from Scott Circle, 6 blocks away.
Get closer.
Combine this with the whole “stop centering people’s heads in your photos”, and you can actually get quite a lot in your pictures.