Being a sales manager is a tough job, especially when you’re promoted from within the company. This happened to me years ago. I was an award-winning sales rep for a consulting firm and was promoted to sales manager. Now my colleagues (and friends) were reporting to me. I knew them well and thought we would be a winning team. Boy, was I wrong!

The average tenure of a sales manager is less than two years, according to Top Sales World CEO Jonathan Farrington. For sales managers who are promoted from within, it’s less than 18 months.

And I quickly found out why…

Off to a Rocky Start

Becoming the boss wasn’t easy or much fun … at least not at first. I had to set goals with each person and hold them accountable for meeting their quotas. It was my job to make sure they did their jobs well, and to point out when and where they needed improvement.

Translation: I was no longer anyone’s friend. One person even yelled at me, and she finally quit.

In hindsight, I realize that I hadn't set realistic expectations for our new relationship. I never sat down with each person and discussed what they needed from me, what I needed from them, my responsibilities as sales manager, and the best way to relate to each other given this new dynamic. I never acknowledged that moving from a peer relationship to our new arrangement would be difficult. I guess I thought everything would work out by itself.

It didn't. Instead, I ignored what could happen and was hesitant to deal with confrontation. After all, we were friends. But in the end, I really messed things up with my local team.

I inherited teams in two other geographies, and that transition went smoothly. Since I hadn't worked with them before, we started off fresh—and I had the important conversations about expectations of each other.

Set Up to Fail?

I never received training or guidance on how to manage a team. One day I was a sales rep, and the next day I was a sales manager. Sure, I knew my quota and the quotas of my team. I spoke to them regularly about their pipelines and forecasts. We strategized and set goals. I knew what it would take for them to succeed, but I didn’t know how to help them get there without being “bossy” and upsetting them.

The big problem occurred when one of my reps—a good friend—was lagging behind. (Yep, she's the one who yelled at me and quit.)

I guess it was a good thing, as I now had the opportunity to hire new sales reps. With them, the dynamic was entirely different because I had learned some important lessons about sales management:

• Set the stage in the beginning and lay ground rules for interaction

• Understand each person's weaknesses and manage to their strengths

• Tell it like it is (facts matter and confrontation is OK)

• Pay attention to early warning signs and let people go before things get worse

• Let sales reps fix their own problems (don't jump in because you can do it better and faster)

I will never again underestimate the significance of a rep-to-manager transition. I would even go so far as to advise against managing the same group of people who once worked alongside you. But sometimes those are the cards you get dealt.

Remember to give yourself a break. Change isn’t easy, and it always comes with a learning curve. But make sure your organization provides you with opportunities to learn how to be a sales manager. Ask for training and for help. It will save you tons of time, and you'll make better, more informed decisions.

If someone had told me that, I would have been a better sales manager and friend.

Joanne Black is America’s leading authority on referral selling—the only business-development strategy proven to convert prospects into clients more than 50 percent of the time. She is a member of the National Speakers Association and author of NO MORE COLD CALLING™: The Breakthrough System That Will Leave Your Competition in the Dust and Pick Up the Damn Phone!: How People, Not Technology, Seal the Deal. To learn more, visit www.NoMoreColdCalling.com. You can also follow Joanne on Google+ or Twitter @ReferralSales, or connect on LinkedIn and Facebook.