For your next tour to Italy, you may want to consider these ideas in avoiding large crowds:
Visit Off-Season: July and August are hot, expensive, and crowded. I don't even think of going to Italy at these times. Who wants to spend their tour of Italy waiting in line all day?
Get the Museum Pass: In Rome, it is called the Roma Pass. In Florence it is called the Firenze Card. These pay-one-price cards gets no-wait-in-line (except for security), no reservations required admission into most of the popular sites. For instance, in Rome go right into the Colossuem and Forum. In Florence avoid the crowds by bypassing the line and getting into popular sites with no reservations needed.
Visit at Night or as Late in the Afternoon as Possible: If you think you are going to beat the crowds in Italy by arriving at museums early in the morning - it probably won't work since everyone else is thinking like you. Also, those big bus tours like to get in there early in the morning too. If a museum like the Vatican Museum is open at night, that is the time to go. If you can't make it at night, go later in the afternoon. Venice is loaded with cruise people who need to return to the ships at about 4 pm, so Venice tends to empty out at that time.
For more information on The Traveling Professor's small group tours for adults to Rome, Florence, Venice and other parts of Italy, see www.travelingprofessor.com.