Enjoy your trip tomorrow!
Make sure you wear comfortable shoes, you will be doing a lot of walking especially between the monuments but up and down stairs in the museums too.
Are you going up to the top of the Washington Monument?
When you go into the museums and the Washington Monument they will either x-ray your bags or search them by hand so be careful what you bring.
I have only had time to go through my photos from my first day there, by the time you come back from your trip I should have my photos posted.
Here is a quick one of the main building of the Smithsonian Castle.