"Write about something you love."
Thanks to his much-loved Silverwing trilogy for young readers, the Toronto-based writer has done for bats what Beatrix Potter did for bunnies and what A.A. Milne did for bear cubs.
But he has also inspired thousands of Canadian kids to say, "I'd like to be a writer, too!"
Oppel cautions that it is unrealistic for everyone to believe that they can be the next J.K. Rowling or Kenneth Oppel.
"But if they want to try, I tell them they have to choose a topic they're passionate about," says the youthful-looking 41-year-old, who was one of the marquee names at this year's Thin Air writers festival.
"It doesn't matter if it's a TV show, a video game or a sport. It has to be a subject that engages them."
He also thinks the educational establishment overdoes it with its lesson plans and projects that encourage students to write their own books in class.
"I applaud it as a basic literacy effort, but it's unlikely that more than one or two kids in a school could be a writer," he says.
"It's like telling every soccer player they could be Beckham."
Oppel recognized his calling at age 13. By age 17, while still a high school student in Victoria, he published his first children's novel, Colin's Fantastic Video Adventure.
Mind you, he had good connections. The famed English children's author Roald Dahl was a family friend, and he forward Oppel's manuscript to his agent.
But once he had a leg up, Oppel did not falter. At university in Toronto, he wrote a lot of arts journalism and, as a film student, he learned the ABCs of crafting screenplays.
During his 20s, in fact, while clambering up the ladder of children's noveldom, he wrote movie scripts to put food on his table.
"None of them were ever produced," he notes. "But it's quite possible to earn a living writing screenplays that never get turned into movies."
Oppel published two children's picture books and two more young-adult novels before breaking into the big time in 1997 with Silverwing, an adventure story about a young bat named Shade who gets separated from his colony.
He followed it in 1999 with the sequel Sunwing, then with Firewing in 2002. He published a prequel, Darkwing, in 2007.
He estimates the worldwide sales of the series to be closing in on 1.5 million copies. He is published in Canada and the U.S. by HarperCollins and by Faber & Faber in England.
There was an animated Silverwing TV series for several years on Teletoon and even a theatrical adaptation (which Manitoba Theatre for Young People (MTYP) presented in 2005).
"My goal was just to be able to make a living as a writer," he says. "Since 1997 I haven't had to work at any other jobs."
Oppel, in fact, treats his vocation exactly like a job. Every workday he spends from 9 a.m. to 5 p.m. in his top-floor office in his house in Toronto's west-end High Park neighbourhood.
With three children aged three to 12, he needs a certain privacy. His wife, Philippa Sheppard, is a Shakespeare scholar.
"You don't get inspiration unless you're sitting at your desk ready for it," he says. "Of course, every once in a while I have to check the weather forecast in Cairo and see what else is on the Internet."
Oppel has just published Starclimber, the third volume in his latest series, the Airborn trilogy. In this volume, set in an alternate universe, Canada leads the space race, which involves a giant ribbon to the stars.
He sold the movie rights to Airborn, after it was published in 2004, to Universal Pictures for a six-figure sum. The producers hired two hotshot writers to come up with a script but they couldn't produce anything workable. The project was quietly dropped, but Oppel remains philosophical.
"It was like they rented my intellectual property for a couple of years," he says. "I didn't have to lift a finger."
He is already starting a new novel. But this time he is staying away from fantasy and science fiction.
"I want to flex different creative muscles."
Beyond that he won't reveal any details.
"I haven't even told my editors yet," he says. "They've been trying to get it out of me."