(Since other subscribers have answered most of the other points I am covering only what is left out. )

To put it in one line any PM or even any manager for that matter should be capitalistic in brain and socialistic at heart.

To elaborate on the above statement a PM should stay on top of the work and get it done keeping in mind the triple constraints and not compromise on the work. They should be firm and determined when it comes to getting the work done.

But at the same time they should be very generous when it comes to rewarding and praising the team.

A PM should also learn to separate the people from the problem. Feedback be it positive or negative should be directed at the behaviour and not at the person.
For eg :
Positive feedback :

I am very happy that you solved the problem quickly. That's great (Correct).
I am very happy with you. You solved the problem quickly. You are great. (Incorrect).


Negative feedback :
I am concerned that you came late to the meeting and that you did not raise the issue on time. (Correct).
You came late to the meeting. You also did not raise the issue on time. I am upset with you. (Incorrect).