We often joke about how we ended up as business partners.

Neither of us had any interest in a business partner, given our past experiences and seeing how bad it can get. Once you've had one bad partnership, it is difficult to justify getting back into another one. Furthermore, as self-professed alpha females, we both have a history working better with men than with women during our careers.

So how did we end up as business partners? How do we manage to make our partnership work while others have not worked out so well, like the co-founders of ZipCar?

It is difficult to write about business partnerships without sounding like a couple of newlyweds, marriage counselors or divorce attorneys. Business partners are human and have a personal relationship as much as they have a business relationship.

The challenge is balancing the human individual needs with the needs of the business. This is no easy task for a single company owner, and the complexity certainly increases as you add other owners to the equation.

While we are women owners of a growing business, the lessons learned are relevant for anyone in a partnership or thinking about creating a partnership.

Common values matter

We first met when working together on a nonprofit board. You can get to know someone's true character in how they commit themselves and make decisions in a situation where they are not being financially compensated.

While serving on the board, we were faced with some challenging and morally questioning situations where we discovered we shared the same core values. Fortunately, through a series of company reorganizations and a management buyout, we are now 50/50 partners and have the opportunity to work together more.

Capitalize on your individual strengths

Both of our areas of expertise were different. One loves to do the things the other hates. It doesn't mean it's a match made in heaven, but it did make us compatible in some ways and more challenging in others.

Kristen is at whiz at execution, and Pamela has always had a vision of where the company should go and how to grow it. Based on our individual strengths and affinities for what we love to do most, we divided up our responsibilities and accountabilities accordingly for managing and growing the company.

Though we agree on a lot of things, it is impossible to agree all of the time, and we often agree to disagree. We have to trust each other's expertise within our areas of accountability, and that partner gets the final say, but not until we have each listened and had a chance to present our case to each other.

Trust us, this is not easy for two senior executives who are used to running the show and getting their way most of the time.

It isn't about being friends

When growing a company, tough decisions need to be made. We are living proof that you don't need to be personal friends in order to be business partners.

In fact, if we had met in a social setting, it is doubtful that we would have exchanged phone numbers and gotten together afterward. It is our agreement to do what is best for the company and our core values that makes it work, not being personally "likable" to each other.

Plan for the end at the beginning

When starting a business, the first thing any advisor is going to ask you is, "What is your exit?"

Before we purchased the company, we knew what each other's exit plans were and the personal and professional goals that contributed to it. As things change, which is inevitable, we often come back to that conversation and make adjustments for those changes.

Though we may have different end games for our personal and professional lives — did I mention there's a 20-year age difference? — we need to be on the same page with the end game for the company since every plan and decision we make leads to that end.

Be cognitive of your self-awareness

You need to be able to admit things to your business partner you sometimes may have a tough time admitting to yourself or your spouse. You each need to understand what your weaknesses are and what is driving your wants, plans and decisions.

In fact, a study conducted in 2010 by Green Peak Partners and Cornell's School of Industrial and Labor Relations said, "A high self-awareness score was the strongest predictor of overall success. This is not altogether surprising as executives who are aware of their weaknesses are also more able to entertain the idea that someone on their team may have an idea that is even better than their own."

This type of partner does not always try to get his/her way but instead looks at the facts and makes decisions without emotions getting involved.

Communicate often

Last but not least, we communicate with each other frequently. It is not always easy since we live and work 2,700 miles apart. But, interestingly enough, this has not interfered with our partnership because no matter where we are, we keep each other updated.

Regardless of how important or unimportant it may seem, we do our best to keep the other fully briefed. The key to good communication is to make sure that there are no surprises.

We don't always need to be thinking the same thing, but we always need to know what the other is thinking. Partners are not mind readers as much as we want to think we are. We cannot stress communication enough. You should always be having more actual conversations with your business partner than the ones you have in your head with the individual.

Every partnership has its challenges. It is how you each decide to overcome them and how you handle them that makes the difference and sets the example for the rest of your company.