My suggestions are based on observations of visitors to my area (Northern VA/DC):
- If you plan on doing a lot of walking, wear comfortable, sturdy, supportive, closed shoes. I know flip-flops and sandals are cool and fashionable, but they are dangerous, especially given the escalators and slippery marble in this area.
- Please dress appropriately for the climate and weather. If you are visiting an area that is hot and humid in the summer, denim is really not a good idea. A hat and your hydrating drink of choice are also good ideas.
- If you visit an attraction that has a security checkpoint, making jokes about terrorism or bombs is a very bad idea and will earn you a great deal of official attention that you will not enjoy.
- If you are visiting a popular destination, area or attraction, realize that you are not the only one interested in visiting that location. Expect crowds and please remember your crowd & queue manners.