When we decided to start writing a column for Inc.com, we knew exactly what our first piece would have to be about: Picking the right partner. There is nothing—and we mean nothing—more important to the success of your start-up than finding the right person to work with.

We've always loved Jim Collins's concept of  "the bus." Basically, people who build great organizations make sure they have the right people on the bus, the wrong people off the bus, and the right people in the right seats. Only then do they figure out where to drive the bus.

As for us? Well, there were only going to be two of us on this bus. Everything was riding on our partnership working. Thankfully, is has worked beautifully. And we credit that to our partnership passing three very important tests.

The Best-Friend Test

We are great friends. We went to each other's weddings, we've traveled together, along with our husbands, and our babies play together. But we're not quite best friends. We met through work, and that has always been the foundational point of our relationship. Seeing someone at work is different from knowing someone socially. Julie had seen Lee hit deadline after deadline. Lee had seen Julie take a room full of editors and art directors with completely opposing visions and get them all on the same page. We've disagreed and compromised. The beautiful thing is that having that history, now when we disagree—and even the best of partners do—it's not loaded with emotional baggage that it might carry with a close friend. And the facts that we came from different parts of the country, different high schools, different colleges, and have different interests, mean we have vastly different networks to draw from. Now maybe everyone doesn't have a decade to spare getting to know someone—and that's fine. But our suggestion is to look for a partner beyond your social circle—and before you commit to something big like a start-up, try teaming up on a smaller project to see if you're well matched.

The Houseguest Test

You know how there are some people in life who you adore, admire, respect, maybe even think they're brilliant...but if they were to stay with you for more than two nights you might lose your mind? Well, your new partner is going to be something like a houseguest that moves in permanently. You will be stunned by the amount of time you spend working on your start-up. The hundreds of hours you spend together on the phone, the thousands of emails, the dozens of trips. If your partner has the potential to get under your skin even a little bit, you're going to be in big trouble. Think about it this way: If you wouldn't want this person moving into your spare bedroom for the summer, don't go into business with them.

The Spouse Test

It's said that forming a partnership is like a second marriage. So perhaps it's not surprising that we each ended up with a business partner that shares many similarities with our respective spouses. Lee's husband is a champion brainstormer—just like Julie. Julie's husband is a detail oriented perfectionist—as is Lee. That underscores an important point: we picked someone to work with that has skills that complement our own. With only two of us running Altruette, we had to cover as many bases as possible. Julie's love of meeting new people and networking is vital to our business, as is Lee's glee at making sure each spec sheet is picture perfect. One of the questions we're asked the most is how we divide our responsibilities, and the truth is: we don't really have to. We're both so clearly good at different things that nine times out of 10, it's obvious who should handle which job.

As for the few tasks that neither of us are keen to do? Well, that's when we're glad we're not negotiating with a best friend, a bad houseguest, or yes, a spouse.