Library of Congress
The Library of Congress (LoC) is at the Capitol South Metro station on the Blue Line. When you exit the station, you will see the LoC Madison Building on your right and the Jefferson Building, the main library, just beyond it. Walk to the Jefferson building and go past the line of tourists. Tell the security guard that you're a researcher and you can go right in. Get directions at the information desk for the Local History and Genealogy Room (LHGR). Ask how to obtain a reader identification card; you'll need it to work in the LoC.
Be sure to take a look at the Main Reading Room, it will take your breath away.
Plan your research ahead of time by going to the LoC website (http://www.loc.gov) and printing out the titles, authors and call numbers of the books you need to consult. If a book says LHGR Ref, you can read it off the shelf, you don't need to have it brought from the stacks.
In the LHGR, fill out several call slips and hand them to the library assistant. Keep the back copy for yourself. Consult books off the shelf while you wait for your books to be brought to your table; it usually doesn't take very long. Don't be afraid to ask for old or rare books, they don't mind giving them to you to read.
There are electrical outlets at the tables in case you want to plug in your laptop. You cannot eat or drink in the LHGR, and there are a great many security cameras.
There's a vending room near the LHGR, but it has no tables. To sit down and eat, you have to go halfway back through the Madison Building. The librarian will give you directions.
To make copies, you buy a card from the machine next to the copier. Bring small bills; it doesn't take credit cards. You make the copies yourself.
One day isn't enough time to accomplish very much. Plan two or three days, one to get oriented and the rest to buckle down and get things done.