Whenever possible, avoid driving in a car. Local journeys can be made by walking or cycling, and always look for public transport routes when travelling further.
Obviously, these options are not available to everyone depending on personal circumstances, but cycling and walking will keep you active and help the local environment.
Share rides, if you have to travel by car, investigate the possibilities for carpooling with friends and neighbors, sharing journeys for work and leisure, thus reducing the number of cars on the roads. Many busy offices actively promote such schemes so ask around to see if you can take advantage of this.