Make sure nothing is blocking the flow of air coming from the air conditioner such as furniture, drapes or lamps.
Make sure the air flow from the outside rear grille is not restricted. This may cause the unit to cycle off due to compressor overload.
Use the Electric Heat option on models that offer this feature. This turns off the heat pump (on models so equipped) and will warm the room with electric heat only.
Adjust the air directional louvers upward to promote improved airflow.
Check all windows and doors. Make sure the windows and doors are closed and have a good seal to prevent drafts and heat loss from the area being heated.