First Day as the New Leader
Whenever you are taking over a group, business, or even a corporation, your first day as the new guy is important and the goal is to set the tone of your management style. If you are managing a small group, you need to setup a group meeting as soon as possible to meet with them. If it is larger than you meet with the managers of the group first, then eventually have a general meeting.
The important objective for any new leader is to convey your goals, objectives, and performance expectations. It is best to initally come across as tough and even demanding. People will respond to that very quickly. As you work with the group, you can gradually taper off on your demands. It is easier to do it this way then the opposite. If you come across as trying to be everyone's friend then decide to crank up the demands, it would be harder. This is how drill sargents work in the military. They come across as hard and even unreasonably demanding initially. Eventually as your training progresses, you will start to understand that they actually care about you. Drill sargents ride you to make you into a better soldier so that you dont compromise your group or yourself when you you need to perform. This same philosophy should apply to being new leader in a group. The group has to perform otherwise you will put your group and yourself in the spotlight if performance drops off.
The biggest challenge is when a member of your group gets promoted to take over as leader. You had worked along side with your colleagues for years, often going to dinners together and even get to know the spouses. As the new leader, it is important that you need to set the tone early. This would entail having your first group meeting with an explanation that even though you were colleagues, you are now direct reports and you have to perform. Now having worked along side with them, you know the strengths and weaknesses of everyone. This should give you leg up in helping you manage the group. In that HBO series "Band of Brothers", Sgt Lipton got a battlefield promotion to first lieutenant. Toward the end, he was reassigned to another group. The thinking is that the army feels that you may not lead as effectively as an officer as you would as a platoon sargent.
Best you can turn the heat up early as the new leader, as you can always back it down later as the groups performance meets your expectations.