lights flicker sometimes in my apartment
I'd contact the landlord/superintendent/maintenance, and have them investigate. 

Electric water heater, electric heater, hair dryer, curling iron, vacuum cleaner. All these devices can draw large amounts of current, which can cause voltage drop leading to flickering lights.  Depending on how the building is supplied, the problem could be caused by your unit, another unit, or a combination.

The problem could also be caused by excess moisture generated by showering, a loose wire, an old dying bulb, a loose light socket, etc.