I followed the "classical" form that I was taught for the most part Khalil Bodhi
First send metta to yourself, wishing yourself freedom from harm, peacefulness and complete Awakening'
Then you hold in your mind a real living person that you are fond of, some teachers suggest that it should be a person of the same sex, or if gay, a person of the opposite sex, its a question I think of not conflating things here,and sending them metta, freedom from harm peace etc.
Then hold in your mind a person to whom you have neutral feelings , and send them the same metta etc.
Then you do the same while holding thoughts of someone you have negative feelings about, you send them metta etc.
Then your family and household.
Then your neighbourhood.
Then your nation.
Then your continent.
Then the whole world.
Then all sentient beings in all universes. Wishing them all joy and peace, freedom from fear and complete unexcelled Awakening.
Another practice I was taught that is more informal and less canonical is when in the car or train or in any situation see that same situation through the eyes of the other people around you. See yourself as they see you. Send them metta and yourself metta through them.