Tourism spikes in the spring in anticipation of the blooming cherry blossom trees. But DC residents know that spring is fickle, and weather can be cold; the trees do not always bloom on schedule. Much better to go in the fall, when it’s a pleasure to be outside, and changing leaves color the city.
Always make a restaurant reservation, even at lunchtime. Business lunches are part of the workday, and spontaneity is often frustrated. Best advice is to plan out your itinerary before you go, and have the concierge at your hotel make the reservation.
Check out the museum gift shops—the Newseum, the National Building Museum, and the International Spy Museum have great ones. Budget enough time to tour the museum and do some shopping.