Keep up with all maintenance.
X2 on check the tires. Make sure the engine is properly tuned and the wheel alignment is correct.
Your mileage sounds about right for the car so I don't think its much off tune, but it never hurts to check.
Otherwise improving mileage is up to how you drive the car, a light right foot pays dividends. I just got back from a trip to visit my sister 300 miles away. Going there I was in hurry so I put my foot down and had to stop for gas after 250 miles, returning I cruised at 60mph and made it home with the tank still a quarter full. Both journeys took roughly the same amount of time, stopping for gas cancelled out the time I saved by driving faster.