Director Dan Scanlon learned a few things making Monsters University, the Pixar prequel that takes Mike and Sulley back in time to their college years. Here, he shares his study notes ...

1. When you do a prequel you already know how the story ends. Work with that.

"You have to really embrace the fact the audience knows the ending at the beginning and you have to choose a story where knowing the ending is good for the telling of the story. Early on, when we started talking about whether to do a film, we did decide we could do a film that was more about the relationship of Mike and Sulley. The best way to know about them was to go back in time."

2. Get the same guys to do the voices of the lead characters. Even if they are 12 years older.

"They [Billy Crystal and John Goodman] were both super-excited at working together.

"We recorded them together as much as we could. It makes such a big difference for them to be able to riff together. [Recording more than one character at a time] doesn't always work in animation. But it really works with those guys."

3. Get in some new distinguished voices in as well, like Dame Helen Mirren as the scary College Dean Hardscrabble.

"I was very intimidated at first but she was so easy ... the first day we recorded her over and over again because she wanted to try different takes and I wanted to try different things. She was very much into the idea of working it out until we found a take on the character we both liked. When takes a role she takes in incredibly seriously."

4. Use the many advances in animation technology from 2001's original. But hey, you don't have to go crazy.

"Yeah, it's funny we wanted to take full advantage of what technology can do now but we didn't want it to look totally different. We wanted to make sure no matter how the world is lit and rendered, our character designs still had a kind of the deceptively simple look for the first film."

5. Hair loss comes to us all

"In the first movie Sulley had 2.3 million hairs and now he has five millon or something, So if you think about it and watch the films in the correct order, he lost a couple of million hairs as he got older. As did we all."

- TimeOut

Follow @nzherald_ent on Twitter for all the latest entertainment news.