Arrive in September when the city is cooling down to take part in the Nile Festival Day and the International Festival for Vanguard Theater. Take a long ride east to Hurghada on the Red Sea for the International Wind Surfing Competition.
Take advantage of the mild winter and visit in December. During this month Cairo hosts the International Movie Festival and the Nile International Rowing Festival.
Spend a day at the Egyptian Museum, located near Cairo's focal point: Tehrir Square. Here you'll find art and artifacts from ancient Egypt (including famous Tutankhamun and revolutionary Akhenaten) to the late Middle Ages.
Barter and shop your way through the hectic but friendly Khan-el-Khalili Bazaar.
Contemplate the inexorable march of time among the awesome Pyramids of Giza. You'll want to visit the recently restored Sphinx, located on the southern edge of Cairo. Be aware that the horse rides around the pyramids and the tunnels within them are disappointing.
Visit the medieval fortress called the Citadel. It was the seat of government for seven centuries; it has three massive mosques and several modern museums.
Enjoy dry weather year-round in Cairo; the only reliable source of water is the Nile. Winters are mild; spring and fall are nice too. Beware of the hot, sandy Khamsin winds in April and scorching summers. The average summer high is 98 degrees F and the average winter low is 47 degrees F.
Check out what festivals, attractions and live performances are happening (see below).
Take care of your flight, transportation and accommodations (see Related eHows).
Check the weather forecast for Cairo shortly before leaving, and pack accordingly.