Are you talking about people managers, or about task managers?
Sometimes a person has the job of both, other times that gets split where one person manages the tasks that are worked on and ensuring schedules are met (often mingled with the job of a producer) while the other manages the people involved, the human element rather than the task element.
For both of them, good team managers serve as a filter for the team from the rest of the organization.
They are the linebacker. When someone comes to the team, your job is to tackle the incoming requester to the ground and prevent them from reaching your star players. You stop them from going through, intercept their request, search for ways to avoid the request, and only if necessary add the request to the future work backlog.
For the people managers, good team leaders are constantly looking for feedback to improve processes. Part of this means frequent one-on-one meetings with each person on your team. Encourage them to give you feedback about you and your job even if it is negative. Hold the meeting weekly if you can, every other week if you absolutely cannot. Schedule enough time that you can work out all the concerns, even the minor concerns, about illness in the family, dealing with anything and everything the team member feels has any importance at all. Even discussions about their hobbies outside of work, that is important. At the end of the meeting you should be discussing things like movies and sports events. If you don't reach that point, if you're still talking about workplace concerns or life concerns or work/life balance concerns, the one-on-one needs to keep going.
Part of improving the process means making experiments and listening to suggestions. If the team is currently using some software to run their sprints and they suggest moving to a paper version, consider spending the money to get a giant magnetic board put up, investing in a thousand magnets and bunches of cards, and going with that suggestion for a few months. Or reverse of that, if they express interest in moving to a specific software because they claim it will do better, be willing to improve the process on their behalf.
Be seen fighting for them in all causes. While you are defending them from other parts of the organization so they can do their job, you are also their spokesman and advocate in getting changes made for them. For either side, managing tasks or managing people, everyone in the organization should know that you are the advocate for the team; you will staunchly defend them from feature creep, you will aggressively slash and cut to reduce things down to reasonable scope. And don't you dare ask the team for overtime when you cannot be there. The fastest way to losing all moral authority with a team is to tell them to work but you be missing. If they're working overtime it means you are there with donuts in the morning, dinner at night, and large boquets of flowers for them to give their wives or girlfriends as consolation. (Yes, seriously. Find out who has a significant other and provide them with two dozen roses)
Then read the books Tom suggested and do the opposite of the bad things listed in them.
