Renting a bus can be costly in the Washington DC area. Budget accordingly.
Vehicle traffic is very heavy, and roads are congested throughout the day, especially during rush hour.
The Mall is much larger than it looks on a map, and the distance between the Capitol Building and the Lincoln Memorial tricks many first time visitors. Plan you time and transportation methods accordingly.
Get started early in the day. Crowds are smaller earlier in the day, which will allow you to explore sites more freely.
Most major Washington museums have security check points with metal detectors. On busy days it can take a while to get through security.
April-June are the busiest months for field trips. Add to this time frame the National Cherry Blossom Festival, and vacationers, this means that the historic sites in the district can be jam packed.
Washington was built on swamp land, which means it can be both hot and humid.
Food carts and trucks around the Mall and other parts of Washington carry a wide variety of food and beverage. Most museums also have cafeterias and snack bars.
Many of the Smithsonian museums carry band aids, sunscreen, umbrellas, and other necessities in their gift shops.