Get everyone focused on thinking about the team's mission, role, and what it takes to get the job done. Drill that into everyone's head and stick to it. Let everything else go.

A mentor once told me that business fundamentally revolves around making money, saving money, saving time, and making customers happier. I like thinking about work that way, as it has nothing to do with religion, sex, gender, age, height, phase of the moon (maybe you employ werewolves), etc.

Focusing on work can be hard though, because it might mean you will encounter a conflict when it comes to supporting a cause with good intentions. Say the MinorityCodingClub wants to host an event in your office. Personally, I think promoting diversity is generally a healthy thing. But what if MinorityCodingClub doesn't allow people not in that minority to participate in the event? You may find part of your staff wants to allow it, and part of your staff opposes it (perhaps silently).

Staying focused on making money, saving money, saving time, and making customers happier. It's hard enough to get people to come together on doing that, so don't tolerate a culture that gets in the way of making that happen.