Having just returned from a wonderful family vacation to DC, I thought I'd share some tips, in no particular order:
1. Avoid driving in DC at all costs. Probably the best thing to do would be to park somewhere in Maryland and arrange to be air-lifted in. I now understand why I've seen so many photos of presidents boarding a helicopter on the White House lawn, but have never seen a photo of one getting into a car.
2. Don't be afraid to ride the Metro. It's cheap, it's clean, and most of the passengers are fellow tourists anyway. So you won't stand out if you look like you don't know what you're doing.
3. Do not visit the monuments in the middle of the day during a summer heat wave. If so, you may end up like one poor couple we met on the Metro. They made this mistake and had to spend several hours at a nearby bar recovering. (We got off the Metro before they did, so I don't know if they managed to make it to their destination.)
4. When visiting the Smithsonian museums, dress like you were going camping in Wisconsin. You know, it's hot during the day, but cold at night, so you wear layers. In DC, it's hot outside, but freezing inside.
5. If your governor is friends with the president, and you once called this governor a liar on a news program, don't be surprised when you are unable to get tickets to the White House.
6. The International Spy Museum does have an exhibit called "Training to Be a Spy". Going through this exhibit, however, does not actually qualify you to be a spy. At least not a competent one.
7. If you are hungry, do not eat at the Spy Cafe. If, however, you don't mind spending $8 for a "snack", go right ahead.
8. The Old Post Office is a great place to visit. It's right next to the IRS building, but don't let that stop you. The tower has spectacular views of the city, even better than the Washington Monument. And the food court on the first floor is great...reasonably priced (at least for DC) and a wide variety of choices. This is esp. important if you have children who think a gourmet meal is a hot dog with ketchup, and you are threatening to stage a hunger strike if you have to eat at one more place where the server asks, "Would you like fries with that?"
9. Be sure to tour the Library of Congress. Seeing one of the few remaining Gutenberg Bibles and the incredible main reading room are well worth it.
10. After touring the Library of Congress, walk down Penn. Ave to Good Stuff and have one of their milkshakes. It will make you forget the DC heat.
11. Most of all, have fun! It's a great place to visit.