Answer:
Inside a vehicle, use the defroster, which directs air from the blower to the windshield, to evaporate the condensation. Condensation forms on the warm side of a pane of glass (or other surface), so using cool air will clear it faster and keep it from returning.
Inside a home or office, this can be more problematic, but use of automotive defogging solutions can help. Defogging solutions contain oils which prevent condensation from adhering to the glass. It also works on cars.