The 737 FCTM has this to say if the overspeed occurs in high altitude cruise flight:
'When correcting an overspeed during cruise at high altitude, avoid reducing thrust to idle which results in slow engine acceleration back to cruise thrust and may result in over-controlling the airspeed or loss of altitude. If autothrottle corrections are not satisfactory, deploy partial speed brakes slowly until a noticeable reduction of airspeed is achieved. When the airspeed is below VMO/MMO, retract the speed brakes at the same rate as they were deployed. The thrust levers can be expected to advance slowly to achieve cruise airspeed; if not they should be pushed up more rapidly"