When and where to place a vapour barrier on a studwall?

Need some advice. I'm renovating my internal garage. We've taken out the old garage door and bricked it up with a window in it. I've studded all the walls and put batts of rockwool insulation in them. I'm going to put plasterboard on the studframe but do I need a vapour barrier on the studframe first? I dont currently have any damp or moisture problems in the room at the moment. Room is 4m by 2m. Two walls are internal (being shared by the kitchen and the living room), one wall is external (window in it) and the final one shares with next doors garage (so internal/external?). Its a minefield of information on the warm side of the insulation versus condensation of the colder side and moldy wood.