start with
100+ Hypermiling / ecodriving tips & tactics for better mpg - EcoModder.com
unfortunately, that mileage could be considered normal for your vehicle. even if you made a 20% improvement, which isn't easy, you would still be looking at 18mpg.
im sure there are vehicles out there that could do the same jobs with better mileage, what do you need your vehicle to do that a small car cant do?