Sunday MBA provides ideas on running better businesses and succeeding in the modern workplace, this week from Harvard Business Review and Heidi Grant Halvorson, associate director for the Motivation Science Center at Columbia University Business School and author of the book “No One Understands You and What to Do About It.’’

When you take your first leadership role, or find yourself at the helm of a new team, first impressions are essential. Come across the wrong way in those early days and odds are you will be dealing with the negative consequences for a long time to come.

Research on perception points to three key mistakes to avoid.

Mistake 1: Act like you know (and can do) everything.

Most people assume that being really confident is key to making the right impression as a new leader. Overconfidence, however, is a very dangerous thing. It can lead you to be underprepared, set unrealistic goals, and generally make bad choices. To make matters worse, when your apparent confidence seems to exceed your competence, you are likely to be the object of derision and scorn.

If, instead, you convey a more realistic sense of confidence, people will see you more positively. In fact, psychologist Tomas Chamorro-Premuzic, author of “Confidence, ’’argues that if you exhibit some modesty, people will add, on average, 20 to 30 percent to their estimate of your competence. Toot your own horn too much, and they’ll subtract the same amount.

Mistake 2: Be too businesslike.

Too many new managers — especially those managing former peers — fear that being warm will make them look weak. But if you want to get your team’s best effort, you are going to need them to trust you. And to figure out if you are trustworthy, people will tune in to two particular aspects of your character — your warmth and your competence.

Your warmth — being friendly, kind, loyal, empathetic — is taken as evidence that you have good intentions. Your competence — being intelligent, creative, skilled, effective — is taken as evidence that you can act on your intentions. Incompetent leaders can’t be counted on, even when they mean well.

You don’t have to “play dumb’’ to seem warm, and you don’t have act like a jerk to seem competent. Engaging in “warm’’ behaviors like appreciating others, listening, and having empathy take nothing away from your reputation as a skilled and capable leader.

Mistake 3: Let them see the crazy.

Years ago, I remember watching an episode of the television comedy “Scrubs’’ in which one character told her friend that she worried she could no longer “hide the crazy’’ from the man she was dating. By “hiding the crazy,’’ she meant keeping a lid on all of the impulses and quirks she had a hard time controlling.

All human beings have their own “crazy.’’ But even though the crazy is part and parcel of the human experience, don’t advertise yours.

This might seem old-fashioned in an era when leaders are encouraged to be authentic and show vulnerability, offices are more casual than ever, and even massive organizations refer to themselves as families. But this doesn’t mean that anything goes. The research is clear: We don’t trust people who appear to lack self-control.

Instead, we trust leaders when we can be confident that they can resist temptation in order to do what’s right. And that, as everyone knows, takes self-control.

Studies show that people who publicly engage in behaviors that are indicative of low self-control — like smoking, overeating, impulsive spending, or being lazy, chronically late, disorganized, excessively emotional, or quick to anger — are consistently rated as less trustworthy. These foibles may make us human, but they don’t help us as leaders.

So, to make the right impression on your new team, remember: Be modest, Be warm, and hide the crazy. If you can do that, you are very likely to end up with a loyal and effective team that is willing to work together and follow your lead.

Reprinted by permission of Harvard Business Review.