You need to take a look at potential trouble spots. Look at the reception area. Don't use the stairs alone. Don't go into elevators with people who look out of place or behave in a threatening manner. If you're on an elevator with someone who makes you nervous, get off as soon as possible, even if it's not on your floor.
Attackers can hide in stalls in the bathrooms.
If possible, restrooms should be in limited access areas or remain locked so only employees or people with permission have keys for access. Don't work late alone. If you must work late, lock doors so non-employees can't wander in, close the blinds so strangers can't see you're alone and use caution walking out to your vehicle when you do leave. As you walk to your car, have the door key or alarm in your hand and ready to go. Look into the car prior to entering.