Better driving means performing any regular maintenance on your car (don't forget to check tire pressures), removing any heavy unnecessary objects from the vehicle (still have the bags of sand in there from winter?), and accelerating smoothly. It also involves cutting your speed on the highway a bit. When driving around town, don't accelerate to a red light (the more you use your brake, the more energy you are wasting). Other techniques include using your A/C less, planning your trips to minimize stops, and turning off the engine instead of idling (new cars are very efficient at starting up, here's a good article on it).

Continue to track mileage to see what the changes are doing to your mileage.

Make the behaviors (and mileage improvements) permanent. Continue to try get better and consistently raise your mileage. This is an ongoing thing, but once you feel like you've made a significant improvement, you can check off the guide.