I love living near Washington, DC. I know that people look at me like I have antlers when they hear that I love this area, but it's true. There's a ton of great stuff to do, all within a relatively small area. Often, when folks come up to visit my wife and I, they want to go to DC, but don't have a lot of time.
Now, I love DC. There's a ton of great food, a ton of great things to do that are mostly cheap or free, and the city is relatively well laid out. I could (and have) spent countless days just wandering areas that I've already been to and discovering new things. But even if you've only got a little bit of time, you can still fit in a lot of the touristy things that make DC such a cool place to visit.
Things to see
First things first: expect to walk. A lot. An average "6 hour tourist" day in DC usually works out to about 7 miles, all of it on foot. I suppose that technically you could hail a cab, or call an Uber, but part of the charm of DC is that the tourist areas are really walkable, especially if the weather is even remotely nice. But you definitely will want some good walking shoes.
The National Archives
Since I'm normally coming into DC on the Green line of the Metro, I tend to get off at the Archives metro stop, which makes the National Archives a great first stop. On weekends, there can be a bit of a line to get in, but it's worth it. The rest of the Archives is great, but if you're on a time crunch, the real piece de resistance are the Declaration of Independence, the Constitution, and the Bill of Rights. There's not a ton to be seen with them, because it's often crowded, but it's the only place to see those original documents, so stick with it.
The National Gallery of Art
If you're in to art, stop in to the National Gallery of Art, right across the street from the Archives. They rotate their art fairly regularly, but there's always something great to see there. Last time I went in, I spent a lot of time walking through the Impressionist galleries looking at the plethora of Monets they have there. But as I was walking back out of the Gallery, I actually stumbled over a gorgeous Mondrian and a Picasso. There's just so much incredible art to be seen there, and they're always changing it up.
The Museum of American History
If you leave out the west door of the Gallery, you start walking straight towards the monuments, the Natural History Museum, and the Museum of American History. Skip the Natural History Museum until they finish their renovations to the dinosaur section. Head on over to the Museum of American History and check out the Star Spangled Banner.
When I was a kid, I lived in Northern Virginia, and we used to come see the folks at the Smithsonian restoring the flag, and the exhibit that they put together once the restoration was complete is a great way to see, like the Archives, a one of a kind part of American history. As with most of the other Smithsonians right now, they're renovating a lot of the American History museum, so you can nicely pop in, see the flag, and head back out. There's just not a lot else to see for the next few months.
If you keep heading west, you head towards the monuments: the Washington Monument, the WWII Memorial, the Vietnam War Memorial, the Korean War Memorial, and the Lincoln Memorial. There aren't any real tips or tricks to these, but I always enjoy walking through these incredible monuments and memorials to things from the past.
Also, I always stop to sit on the Lincoln Memorial steps. Partially because it pretty well symbolizes the end of the tourist experience, but also because it's a great view. Also, for a nice view of Arlington Cemetery, walk around the back side of the Lincoln Memorial.
Wrapping Up the Day
I have a confession: most of the time, by the time we reach the Lincoln Memorial, any guest with us is pretty well beat. I usually end up calling an Uber to pick us up at the Memorial. I'll often ask them to drop us next to the White House. As with anything else in DC, the side you think is the front is actually the back, and is the better looking side. Once you go and look through the fence at the White House, it's only a few blocks walk back to the Green Line, bringing you back in a nice circle.
There are some glaring omissions to this particular tourist trip of DC, and that's a bummer. First, the Museum of Natural History is undergoing renovations right now, and there's really not a ton of cool stuff to see there at the moment. The Hope Diamond is neat, but often very crowded, and kind of a pain to get to. The Air and Space Museum is great, but it doesn't really hold up to the newer museum out near Dulles, so I only go if I'm with someone who is really in to planes and rockets. And the Capitol is neat, but it's a really long walk down and back, and there's not a lot to see down at the Captiol end of the Mall, so I usually skip that as well.
And that's a pretty full day. It's not everything in DC, it's just a small glimpse, but it still provides a great look at the cool monuments and museums that make DC one of my favorite cities.