Make sure you get a good one that would given correct readings because electromagnetic disturbances can shift or deviate the needle resulting in wrong readings.
A compass is a very sensitive instrument and you should avoid using it near materials containing iron, electrical appliances, iron grills or even in a car.
Stand inside your office or house facing the main door, with the compass in your hand. Take three readings of the compass direction and establish the direction the main door is facing.
For the third reading, stand six steps outside the main door, with the door now facing your back.
The average of the three readings will now give you the direction your house is facing. In most cases, all three readings will be the same.