If your neighbors are also without power, call your local power company.
Use a flashlight or battery operated lanterns.
Do not use candles for emergency lighting. Candles and kerosene lanterns are fire hazards.
Turn off major appliances. They could overload electric lines when power is restored, causing a second outage.
Use portable generators cautiously. Make sure they are outside in a well-ventilated area. Always follow manufactures recommendations for operations and refueling.
In cold weather, drain pumps, supply lines, water heaters, and boilers. These can freeze when the power is lost. So can traps in drains of tubs, sinks, commodes, washing machines, and dishwashers. In order to avoid burst pipes, close the main water valve and open the spigots and supply lines and drain them.
In advance, provide your power company with a list of all life support equipment required by family members. Develop a contingency plan that includes an alternate power source for the equipment or relocating the person.