Gas Milage

OK, this is boring stuff but I wanted to have things noted. I got 10 gallons of gas after going 185.5 miles. That give milage of 18.5 miles per gallon. Not too bad, but it really should be about 21 to 23. I have some work to do. Need to get the idle down to 900 RPM or so instead of 1500 RPM.