I became a manager before I knew how to lead effectively. Here's what I wish someone told me before I was promoted.

• James Monroe is the author of "Don't Be a Dick Manager: The Down & Dirty Guide to Management."
• Managers are often promoted into their positions because they're good at something else — but that doesn't necessarily mean they're good at being managers.
• Some managers learn how to be great at managing, but many others don't, which can take a heavy toll on businesses.
• Here are 8 things that all new managers should know.

Like every new manager I've ever known, I was promoted into management because I was good at something else. I received neither training nor mentoring, but the fates of several hard-working people were suddenly in my hands.

My previous bosses had set examples, positive and negative, but really, I had to figure things out on my own.

Some new managers do eventually figure it out, and they end up fine. I did, but only after leaving a trail of mistakes and regrets in my wake. Many new managers — most, according to Gallup — never figure it out. They end up unhappy and insecure, which turns them into lousy managers who make their people miserable.

The impact on the bottom line is significant. Gallup estimates that unqualified managers cost US businesses hundreds of billions of dollars annually. Yet, we still don't understand what it takes to be a skillful manager, and we still don't equip our new managers for success.

So here, after years of trial, error, and some very gratifying wins, are the eight things I wish I'd known that day when I walked into my new office for the first time:

1. The rules have changed

When you get promoted to management, it's usually because you were good at your old job. But the skills that made you good in that role will not make you successful in the new one. You need to learn how to motivate your team members, manage your boss, and keep your focus on the business. Your success now depends on your team. You need to start learning how to do this job well.

2.You have probably picked up bad habits

Most managers are not particularly good at managing. They can be arrogant and dismissive, and they are often poor communicators. They can focus too much on their needs or on making sure they look good to the boss. And they've been your role models. You have some un-learning to do.

3. There's a massive difference between respect, love, and fear

To succeed, you'll need your team's respect, and you'll earn it through your words and actions. If your employees are afraid of you, they will neither trust nor respect you. If you try to be liked, you will not make tough decisions or have hard conversations. But it's the hard conversations that often earn you the most respect.

4. Your people know more than you do

When you become a manager, you're no longer in the loop. You will not know who's dating who, and you will not get the company gossip. But your people will still be very much in the loop. Everything you do and say will get back to them, along with everything all the other managers do and say. Remember this, and don't say anything in conversations, texts, emails, posts, or messages that you wouldn't want your employees to hear.

5. Your ego is your enemy

OK, that's only true if it's large. If you have a small ego, it's your best friend. But if you don't control your ego, you'll get defensive. You'll take things personally and react to things that you should ignore. You'll base decisions on your ego rather than the needs of the company or your team. And all of that will cost you respect and undermine your success.

6. Your team's success is your success.

You must work hard to make sure each of your team members has what they need to be successful. Your boss will judge you based on the team's output, the quality of their work, and the team culture you create. Your goal is to have a high functioning team that doesn't get distracted by trivialities. This will take effort. It means you will work with each team member to bring out their specific skills, but it will pay off. Because …

7. The better your people look, the better you look

When your team performs, you must praise them loudly and publicly. Recognition makes your people feel great, and it makes you look like a brilliant manager. It doesn't hurt that you'll look selfless and generous too, but make no mistake: people will see a strong, confident, capable manager.

8. Think about what it's like to manage you

Most new managers don't think much about boss management, but it's incredibly important. Managing your boss doesn't mean sucking up; it means making sure that you are in sync with the company's goals. It means giving your boss the information they need to appreciate your team. And it also means helping them to look good to their bosses. Just like the people who report to you, you want to be a high-functioning, focused employee. So, make sure your communication style and your interactions with your boss reinforce that.

James Monroe is the author of "Don't Be a Dick Manager: The Down & Dirty Guide to Management." The book is based on his many years of experience managing teams in media companies and technology startups. James spent most of his career in television marketing and programming, working for CBS, NBC, and other media companies.

He was an early employee of TiVo and started that company's media research business. He co-founded one video streaming startup and worked as the head of product for another. He now lives in Santa Cruz, California, where he writes about management to help new managers avoid the mistakes most new managers make, and to help companies hire and train better managers. His blog is available at http://www.dontbeadickmanager.com/the-dont-be-a-dick-manager-blog/