To save time for queuing up, you may reserve your ticket on internet by paying a few Euros more for each ticket, Or you may join a group tour so that you need not to buy ticket. Now I tell you a special way not only to save a few Euros for reservation, but also need not to queue for ticket.
First, you can buy a ticket for the Colosseo only or you can buy a ticket for all 3 parts. The difference is just a few Euros more. If you will visit all 3 parts within 2 days (yes, the ticket has 2 day duration for you to visit all 3 parts), you should better buy a full ticket.
Now the trick is this, DON"T line up at the Colosseo ticket center to buy ticket. Just go to the entrance of the Roman Forum and buy a full ticket by paying ordinary price, there is no one lining up there. Then visit the Roman Forum and the Palatino first. In that case, you can save the reservation fee and the queuing time. The only drawback is that you will visit the Colosseo later on the day. Crowd control rarely limit the visitors having ticket, it only stops selling tickets to the new visitors.
After visiting the Roman Forum and the Palatino, you can hold your ticket to enter the Colosseo directly, skipping the long line in ticket office.