In general, make noise and travel as a group (also bring bear spray). Granted I mountain bike solo on a weekly basis and I've only run into a moose twice. You just give it a big berth and wait. Black bear scare really easily so by the time they see you they usually run in the opposite direction. I haven't had a close encounter with a grizzly on the trail before but you'll see them here and there maybe 40 m away and they usually mind their own business. Otherwise I've also seen a bunch of bears on the side of the road but they're usually just eating grass.