I live in the U.S. and go to D.C. often.
My favorite, medium priced hotel is the Sheraton National for several reasons. It's located at 900 S Orme St , Arlington, which is immediately west of the Pentagon and sits on a hill. It's also immediately adjacent to the Arlington National Cenetery and one can walk to the Tomb of the Unknowns and watch the changing of the guard... very moving (24/7/365).
Sitting, as it does on a hill, one can see all of the monuments of Washington D.C., especially the Washington Monument.
The hotel will run their shuttle for you (24 hours a day) for a 10 minute free ride to the Pentagon City Metro boarding area. Pentagon City is a large shopping mall and very pleasant. The Metro is the light rail system that serves all of D.C. Most of it is underground, but it surfaces to cross the Potomac River. Very reasonable, dependable and clean. They are especially helpful to tourists, which is the lifes blood of D.C.
Exit a L'Enfant Plaza to visit everything and anything in the National Mall area of D.C. The "Mall" is the area the encompasses all the governmental buildings, The National Museum and National Air Museum (my favorite), The Smithsonian, the National Archives (where the original Declaration of Independence is on exhibit) and numerous other sights.
Here's a link for the Mall
http://www.nationalmall.org/nationalmall.php ...
Lots of great places to eat... just ask around.
Welcome to the U.S.!