Welcome
These tips got me immediate and cheap mpg improvements (assuming you didn't already do them).
We need to know a little more about you with the car. What kind of driving do you do? How much improvement are you aiming for? What are you willing to spend/do for it? Type of transmission?
Also, if you don't already have a way to get instantaneous feedback from your car in MPG, I suggest getting a device that will such as a SuperMID or Scangauge. Even a vacuum gauge can help in tailoring your driving style to be more efficient.