Why did you choose to have Greg and Earl co-workers with films? Why not novels, or poems or art?
Well, it had to be an art form that demanded to be collaborative, so anything like novels or poems or paintings was out. You don’t need a partner for those. But filmmaking forced Greg and Earl to make room for each other, creatively/emotionally/comedically, and I really liked when they did that. Also, the process of making a film is so involved and disruptive and out in the open – it’s kind of the worst possible lifestyle choice for someone who wants to be invisible. So it was the perfect art form to inflict on poor Greg.

Greg devised a system that would keep his invisibility intact whilst he “survived” high school, where instead of just being part of one group of people in high school, he’d gain low level friendship status with as many groups as possible. Where did the idea for this system come from?
Well, I wanted Greg to be cut off from people, but I didn’t want him to be an antisocial loner. I wanted to see if he could combine that cut-offness with a kind of friendliness, too. Because he’s not an unfriendly guy. So out of that came this idea of hiding in plain sight – interacting without ever showing your true self. But it’s certainly not a revolutionary idea. Politicians do it, to cite one frightening example.

What were your own personal experiences of school and what tips of advice do you have for anyone going through high school or secondary school right now?
I went to a really diverse and wonderful school in inner-city Pittsburgh, where all the various groups and types of people got along pretty great, and a lot of interesting stuff was going on all the time – and I still hated high school. It’s just a rough, rough period in one’s life. You look weird, you feel weird, and a sadistic educational system is forcing you to look at aortas all the time. My advice is probably a bit like Mr McCarthy’s: just focus on getting through it. Don’t expect it to be the best part of your life. It’s probably among the worst. Which is actually kind of great! You’re getting it out of the way.

Does any part of the story have roots in your own personal life? Was anything in the book inspired by your own personal tales?
It’s certainly not my story – I didn’t have a classmate or friend who developed cancer. But I was thinking about illness and dying when I wrote it. My grandfather was terminally ill and any interaction with him felt so incomplete. It seemed impossible to say or do anything that was enough. And of course that was true. Nothing could have been enough. You want a storybook kind of closure with someone when they die, but I think that kind of thing is impossible.

I did make films with friends, though. They were homages to comic filmmakers we liked, and their badness was basically infinite. If they ever make it out into the world, I will renounce all ties to human society forever and instead live among a colony of gibbons.

And finally, how does it feel now that Me and Earl and the Dying Girl is now a film?

It feels great. But terrifying. One feeling I have is the same helpless fear-but-also-hope I had when the book came out, which is a little bit the feeling of a parent sending their kid out in the world and knowing they can’t protect the kid if someone wants to punch the kid in the face. I know this is not a healthy way to feel about a book or a movie. But it’s what I feel.

• Jesse Andrews’ Me, Earl and the Dying Girl is available from the Guardian bookshop. The film version, directed by Alfonso Gomez-Rejon, is on general release in the UK right now.