1. Rule number one: do not panic!
2. If your apartment is completely dark, think about how you can provide light. Tip: Your smartphone has a flashlight function.
3. Turn off potentially dangerous electrical appliances such as the stove or iron.
4. Clarify the situation. Look out the window, ask your neighbours, and see who else is affected by the power cut. If several apartments or even the entire blocks of houses are affected, please wait. In this case case, the problem is linked with the general power supply and it might make no sense to call an emergency electrician. Usually the power comes back quickly.