Well, I've managed a few teams in my time (cue crogety old man music), and so I have some insights that can help your design team run (semi) smoothly. Some of these recommendations are applicable to ALL types of teams, and I list them for the sake of completeness.
Have a (realistic) shared vision and direction. Have a mission statement and a set of principles the team should follow, but make sure its pragmatic and achievable. If you pump up your team with lofty aspirations and blue-sky visions they will quickly become demotivated when the hard fist of reality shatters those dreams.
Set a rigid, yet flexible, process. Set a standard design process, based on best practices, so that junior designers can have a guideline to do their jobs and work from. But be flexible about the details of the process if team members come up with better ideas on how to do things…. keeping in mind that "flexible" is not the same thing as "disposable" – process is important, and a repeatable process will increase efficiencies over time.
Spread the love around. Don't play favorites, let everyone have a shot at the big projects. Even if you don't think a member of the team has the ability to do the job well, you have to give them a chance to step up. Just pay close attention and help them when they need it.
Listen and pay attention. You need to be there for the team, and a lot of that involves listening to a lot of complaints and gossip. Encourage and support, be ready to intervene if your team members need help. And try not to "gossip back" if you can help it.
Allow for disagreements, but don't let them get personal. Design teams are passionate, and they will often wear those passions on their sleeves. Let them debate, but don't let it get out of hand (and get in the way of work)… and don't let people insult each other or their abilities.
"You are not the work." This is one of the most important points I can make, which is that designers have to separate themselves from what they have done, because what they have designed will change before it's finally implemented… and you may find through usability tests that the ideas/designs don't work at all. Continuously reinforce that point to designers in your team.
Don't compete, mentor. As a leader of a design team you should never put yourself in a situation where you are "competing" with anyone on your team. When I say that, I mean don't be working as a designer and a manager at the same time, because that could cause jealousy and discord. If you have to step in and work, do it by partnering with a junior team member and use it as a mentoring opportunity as well.
Set up "peer designing." If you have the ability, partner designers on projects. Having two or more people working together allows for the generation of more ideas, the ability for one designer to support or encourage the other when he/she needs it, and allows for "cross-training" while the work is getting done.
Credit the team, not yourself, for successes. If a design project goes well, give full credit to the people who did it. And if things go badly, don't throw anyone under the bus. You are where the buck stops.
Don't play favors (and don't hire friends). Don't spend all your time with just one member of your team, be equitable with how you invest that time with everyone. if you don't, people will be left out and they may not give their all when you need it from them.
It's very tempting to build a team with colleagues you worked with before, because they are a known quantity and you enjoyed working with them before. Don't do it. In my experience, brining in friends to work for you will end up resulting in bad things happening. Because they have worked with you as a peer they'll not respect you as much when you are the boss.
Appreciate that people are different. You are going to have a mix of different skills on your team, and not everyone is going to be the "perfect designer" that you can just throw at a project and let them go. Pay attention and balance out what people do with what they are good at and the most passionate about whenever possible.
Mentor, don't command. You cannot mandate design direction to your team. They are going to have thier own ideas, they are individuals with their own perceptions of the problem space. You may "know" the right approach is to do A, but sometimes the best thing you can do is let the team decide that A is the way to do it on their own (with a little coaching form you).
Allow for regular personal "research time." Unless you are under a crushing deadline which requires "all hands on deck," give your team time to become better designers and researchers by reading articles and books. Make continuing education a necessary part of everyones time. And allow for time for the team to share what they learned with each other (preferably over drinks at a social hour).
Have fun. Captain Kirk once said that the more complex the mind the more important the necessity of play. User Experience Design teams are usually made up of some very smart "complex minds" indeed – always allow for opportunities to explore and play.