Well, all I can suggest are the fairly obvious things:

Make sure your air filter is clean.
Make sure your tires are properly inflated.
Make sure your alignment is within spec.
Use 93+ octane; try different brands.
Use synthetic oil.
Try a fuel system cleaner (such as Chevron's).

But really the best suggestion with these cars is to change your driving style. These cars are a blast to rev high, but if you're wanting the best fuel economy that's the first thing you want to avoid. Some owners swear they can actually see the fuel gauge drop when they rev to redline.