Drew Houston says he relies on an unusual element to guide his  leadership style: paranoia.

"The first thing is having a healthy paranoia for trying to find out what you don't know that you don't know," the founder of cloud storage company Dropbox tells The New York Times in an interview published Friday.

Clearly his unusual approach has worked. Dropbox, which Houston founded just a year after graduating from MIT, now has a reported valuation of $10 billion. Turning the corner on his company's first decade, Houston--a former Inc. 30 Under 30 honoree--offered advice on leadership, hiring, and maintaining a healthy company culture. Here are his three best tips.

1. Be aware of what you don't know

Houston ensures he will keep improving as a leader by continually asking himself a simple question: "Six months from now, 12 months from now, five years from now, what will I wish I had been doing today or learning today?" Typically he fills in those gaps by reading. "I have always wondered why people put so much energy into trying to have coffee with some famous entrepreneur when reading a book is like getting many hours of their most crystallized thoughts," he tells the Times.

2. Surround yourself with people who encourage you to improve

Having a purpose for the business is a must, of course, but the people who fill the office are just as important. Houston says he hires for passion. "I'm drawn to people who really love their craft, and treat it like a craft, and are always trying to be better and are obsessed with what separates great from good."

3. Define your values, and stick to them

As Dropbox moved from an early-stage startup to an established business, Houston wanted to explicitly define the company's culture. To do this, he approached it as an engineering problem. "It seems that most companies, most organisms, decay as they get older and bigger, and so how do you inoculate your company from the most common things that tend to go wrong?" He came up with five ways to fight these problems: Be worthy of trust; sweat the details; aim higher; "we," not "I"; and don't take yourself too seriously.