Maurice Sendak was an expert on the subject of letting one's imagination run wild. The beloved children's author wrote and illustrated more than 100 books before his death in 2012, including Where the Wild Things Are, In the Night Kitchen, and Outside Over There.

In the short documentary Tell Them Anything You Want, which debuts on Hulu on June 15, viewers are treated to a rare glimpse inside the mind of Sendak, who would have turned 90 this month. Co-directed by Spike Jonze, who adapted the writer's most famous book into the 2009 film Where the Wild Things Are, the documentary delves into Sendak's earliest experiences as an aspiring artist, all the way through his work as an author in his 80s. The film reveals how Sendak developed his craft to become one of the most distinguished children's authors of the 20th century.

Here are five tips from Sendak's career that can help you harness your creativity.

1. Start with imitation  

Sendak first learned to draw by copying the work of his brother Jack, who was five years his senior and, according to Sendak, a better artist. "He was the genius of the family," he says in the documentary. Imitating someone else's work may seem like the exact opposite of creativity, but drawing inspiration from the work of another artist when you're starting out can be the first step toward developing your own distinctive style. Jack Sendak would also go on to become an author and illustrator, and had his brother Maurice do the drawings for his first two books.    

2. Only get formal training if you want to

Sendak took classes at the New York Art Students League while working as a window dresser at F.A.O. Schwarz in New York, but he never went to art school. "I drew in a clumsy fashion," Sendak says in the film, adding that his editor Ursula Nordstrom didn't care about his lack of formal training. "She could see beneath that." The lesson? Being creative doesn't require a degree, so only pursue formal training if you really want to. 

3. Don't let criticism discourage you 

Although Where the Wild Things Are sold more than 20 million copies worldwide, the book received terrible reviews upon its release in 1963. The famous children's psychologist Bruno Bettelheim even told Sendak in person that he "hated" his book. While critics certainly have been known to be dead wrong from time to time, the critical consensus is often a good assessment of artistic merit. Whether you agree or disagree with feedback on your work, the important thing is to not let criticism prevent you from developing your craft and continuing to pursue creative outlets.

4.  Set a creative routine

In addition to drawing in the same room every day, Sendak would create what he called "little rituals" for himself. These included simple things like looking out the window and observing the colors of nature, listening to Mozart, and reading Charles Dickens for an hour at night. Creative pursuits can lead to what Sendak called "an isolationist form of life,"  so setting a routine for yourself can keep you engaged and ultimately help to fuel your creativity.

5. Don't take yourself too seriously

Even with more than 100 children's books published, a National Book Award for Young People's Literature, and an honorary doctorate from Princeton, Sendak didn't take himself or his work too seriously. "I am not earth-shakingly important," he says in the documentary. "I am trying very hard to concentrate on what is here, what I can see, what I can smell, what I can feel--making that the important business of life."

For Sendak, finding success in a creative field didn't require having the most talent or even working the hardest. He attributed his success more to his philosophy that children shouldn't be protected from the truth, even if it's sad or scary. "What I've offered is different, but not because I drew better than anybody or wrote better than anybody, but because I was more honest than anybody," he says in the film. "If it's true, you tell them."