Carpool with family, neighbors and friends. Cut down on meat as a protein source. Only a few billion people could eat as much meat protein as the average American. We already have almost seven billion people on the planet. Don't use antibiotics unless you absolutely must.
Many disease strains no longer respond to antibiotics, in part because of overuse.
Volunteer at local schools or homeless shelters or organizations like Meals on Wheels and others that care for the elderly or handicapped. Make sure you are practicing safe sex. AIDS is becoming the number one cause of death among young people. Buy clothes and materials that are manufactured by adult workers who receive a fair wage and work in decent conditions in a non-polluting factory. You must do your homework here, be persistent and ask a lot of questions.