When we did the Vatican Tour, we went to the end of the line, thinking that the line was just up the block. I walked up the block, and saw that the line extended around the corner and ANOTHER block to the entrance! It was HUGE.
The "trick" is to join a tour group. There are always hawkers selling tickets to join an official tour. You pay double the price of entry, so around 30 euro instead of 15 euro, but well worth it not to stand in a queue for hours. Once inside, you can choose whether to stick with your guide, and we had a really knowledgeable one so we did say with her, or go on your own.
Some absolutely astounding sculptures in the Vatican garden. Well worth it (but not worth the loooooong wait...).