A couple other comments:
1. Make sure your tire pressure is set correctly - that can have a dramatic impact on your gas mileage.
2. You don't say if you drive mainly around town, or on the highway. If it is around town, I'd say 14mpg isn't too bad - keep in mind you are constantly having to accelerate a heavy vehicle from a stop, which burns a lot of gas. If that is highway mpg, then it is not too great - I would think you could be at least 10% higher (15-16), and maybe 20% higher (17-18). Start with the things Joey mentioned (tune up, air filter), check your air pressure, drive lightly (no heavy acceleration - try to accelerate evenly and slowly), use the cruise control a lot, etc.
3. You might also try to find gas that is "pure" versus having 10% ethanol in it. I believe ethanol can have a pretty dramatic impact on your mpg.
-Rich