This is a problem that I have spent time thinking about. I don't generally like the term "manager." As pointed out by ERN, you don't "manage" people. They must be led. Leading implies the leader is out front.
Look at the model used by all the branches of the military. They understand that leaders are not born, they are made. They are trained to become leaders. In every branch, should you decide to make the military a career, you will be promoted to leadership positions, owing to an "up or out" policy. But, the military does not promote a soldier, then throw that newly minted leader (sergeant, lieutenant, etc) to the wolves. Before assuming a leadership position, that soldier attends leadership training schools. And at each new level, there is a new school to teach leadership at the level the soldier is about to enter.
Contrast that with nursing. If a nurse wants to become a leader, s/he applies for the position, gets the position, and is thrown into the mix. Today a staff nurse, tomorrow a shift supervisor. Hopefully, s/he will be mentored by another, more experienced supervisor. S/he will make a lot of mistakes, and will learn the position through hard experience. And most often, the employees suffer for the mistakes of the new leader. It is a cycle that repeats itself as the nurse climbs the "management ladder."
What makes a good leader? Lots of things, small and large. Ultimately, a leader has two responsibilities: Accomplish the "mission," and take care of the people. Usually, if the people are taken care of properly, the "mission" is taken care of by the people. So, what qualities go into good leadership?
-Set high standards, and expect the people to meet them. Don't expect them to meet those standards magically, get the appropriate training for your people in order to help them meet those standards.
-The leader must not only meet the high standards s/he sets, but must exceed them. Never ask an employee to do what you yourself will not or can not do.
-Make sure employee needs are met. In the military, this is expressed as "a leader never eats until all the soldiers have had the opportunity to eat." Get your people lunches, breaks, etc. Get the people to work together on scheduling, so that when a nurse needs off for personal reasons, that need can be met.
-Protect your employees. Fight to ensure that upper management does not impose impossible or stupid conditions. Remind upper management of the two goals of leadership.
-Never let employees see you fight with upper management. That's done in private. You must speak with one voice.
-Never reprimand an employee in front of others. Reprimands are a private affair. Rewards are to be given publically.
-Never forget that employees are human, and humans make mistakes. Do not set up a zero defect environment, because no one, not even you, will ever live up to the standard. Use mistakes as opportunities to teach, rather than opportunities to punish.
-Never punish the whole for the actions of one, or a few.
-Above all, be FAIR. A leader can have no favorites. The same standard applies to all, except the good leader has a higher standard for self than for the employee.
-Catchwords: Knowledge, courage, focus, fairness.
The list could go on and on, but I think I have painted a pretty good picture. Its a shame that budgetary restrictions force nursing into a "sink or swim" policy. A good hospital would develop its leadership, so that the new leaders would not feel thrown to the wolves. New leaders would know the basics of leadership, and be expected to apply those principles. New leaders would know they were supported. And employees would know they were protected from the mistakes new leaders would be bound to make.