most mages start off putting points into the fire talent tree, then at around level 30-40, respeccing to frost. it's said that in PvP servers, all mages need 18 points in arcane. this probably isnt true inPvE servers, but i suggest any points you don't end up putting into the frost tree putting into arcane.
there are plenty of guides on the net showing you talent "builds" pre-determined talent point distributions that other players have found usefull, but equally you could do something completley diffrent, like spread your points accross all three trees or become a fire/frost mage :D