Simply driving the speed limit and not driving like a crazed maniac should fairly easily net you 40 mpg.
A manual transmission will give you better results than an auto (you didn't specify what you have). Check out the 100+ hypermiling tips (link up top the page) and pick out a few you like and try them. Once you get used to doing them try out a few more to incorperate into your commute. As you try new things your mileage will continue to increase.