Use effective family planning methods. If you already have children, give serious thought to vasectomy or tubal ligation.
Adoption can help in many ways.
This is the single greatest contribution you can make to the quality of life for all children of the future. Join a conservation organization . Read books and articles on wildlife and environmental issues. The folks at ar-news report that every quarter pound of hamburger we eat destroys 55 square feet of rain forest. Volunteer your time to conservation projects.