Lights that flicker, dim, or do not turn on, even with tightened/replaced bulbs - this can signal a dangerous loose connection or overextension of your home's electrical system.
Outlets that are discolored, or warm to the touch.
A humming sound or burning smell coming from an appliance or area of your home.
Also be mindful of keeping your electrical system and appliances healthy:
Never overload circuits; especially with large appliances.
Replace old appliances, or have them inspected.
Replace damaged, old or cracked cords.
Never use light bulbs that exceed the wattage for your fixture or lamp.