How to avoid the line into the Colosseum is not a hard as you may think.
I have been living here in Rome for 5 years and never once had I to stand in line at the Colosseum. The entrance fee into the Colosseum and the Roman Forum is 12 euro but few people know that it is the exact same ticket. If you go to the Roman Forum 1st around 9am there is never a line to buy tickets. Even if you have little interest in visiting the Forum you can still purchase your ticket there and when you see the long line to buy tickets in the Colosseum you can walk directly past it. You will feel like a V.I.P walking by what is usually a 1hour and 45 minute line. The ticket itself is valid for 24 hour.
Enjoy avoiding the line into the Colosseum.