Last year four Wharton Business School graduates launched Warby Parker, an online eyewear store with a philanthropic bent: For each pair sold, one is donated to a person in need of eyeglasses in Latin America, Asia, or Africa. Here, cofounder Neil Blumenthal (pictured, left, with cofounder Dave Gilboa) shares his tips for how to start a business with friends.

"From Day 1 we committed to each other that we'd remain close friends, so we ensure a healthy working dynamic by creating mechanisms to help resolve disputes and setting up monthly feedback sessions between the four of us."

Always be honest
"Friends going into business together should be thoughtful and considerate to each other but also speak openly. When hearing something critical, it's important to presume positive intent—after all, you're friends, which is why you went into business together in the first place."

Avoid stepping on one another's toes
"Having clear areas of responsibility is super-important. The two of us run the business day-to-day as co-CEOs, and our cofounders, Andrew and Jeff, are on the board of directors, but they have other jobs. The distinction allows us to coordinate our efforts and be productive."

Don't make it all about business
"The four of us talk on the phone about work and have our board meetings, but we also hang out socially at least once a week."

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