When new managers hit the ground running, it makes HR’s life easier. Good managers keep your brightest stars engaged, which improves retention and keeps you from having to fill talent gaps. Poor managers — or at least those who start off poorly — have the opposite effect. 
Below are three common, but avoidable, mistakes new managers make that prevent them from starting on the right foot.
They come from Heidi Grant Halvorson, Ph.D., associate director for the Motivation Science Center at the Columbia University Business School. Halvorson, who’s also a best-selling author, shared them in her column for the Harvard Business Review.
They are:

1. Being overconfident

Confidence in one’s own abilities is important, but being overconfident can cause a manager to be under-prepared and set unrealistic goals.
Plus, overconfident people tend to be unpopular because it annoys employees to hear someone talk a good game but fail to back it up with actual performance.
Halvorson says one of the best ways for managers to earn the respect of their peers is to exhibit some modesty with respect to their skills and abilities. In other words, you want managers who exude confidence — without it rising to the level of cockiness.

2. Being too cold, or businesslike

There’s a perception out there that being warm – by encouraging others to talk, making kind gestures and offering compliments – makes you seem weak.
Not true. It makes employees feel like you have their backs.
So showing some warmth can play a key role in building trust with employees.
Halvorson says employees tune in to two aspects of a manager’s character right away — their warmth and their competence.
Competence is key because without it a manager can’t be counted on — whether they mean well or not.

3. Failing to keep emotions in check

It’s essential for managers to act professionally — that means making sure they aren’t quick to anger and don’t rush to judgment when problems arise.
Employees have a difficult time trusting those they feel don’t have control over their emotions.
Halvorson says everyone has their own unique brand of “crazy” — the impulses and bad habits we know we shouldn’t give in to (because they’re destructive) but do anyway. And even though it’s something everyone has, she advises managers to do what they can not to “advertise” theirs.
In other words, managers must work to keep their impulses private. Employees don’t want to work with someone who appears to lack self-control.