Maintain proper tire pressure. K&N air filter decreased my mpg summer and winter, but more hp. I made a cover similar in shape to the one in this link.

http://ecomodder.com/forum/showthrea...d-cap-583.html

They are sometimes referred to as whale backs. Mine is a frame covered with vinyl. Maxed out so far at 26.5mpg in a 99 Nissan Frontier V6. Almost 500 miles on an 18 gallon tank. Gotta like that!