Sure, you might vaguely remember what miles per gallon rate the nice salesman told you your car got before you first drove it off the lot. You might even still have the owner's manual that tells you such information. Well, let's say you're like me, and you forgot/lost the manual years ago. Come on—there are more of you me's out there than you'd like to admit (nominated for most confusing sentence I've ever written that I refuse to edit).
There's an easy solution over at American Cars Fuel Economy. Just pop in the make, model, and year of your car, and the incredibly dated-looking yet surprisingly informative website will cough up more specifics about your car than you'd ever care to know. Most importantly, it'll tell you what MPG your car actually gets in highway and city driving.
Once you know that, then your trip towards more efficient driving really begins. You might be startled to discover that your little Civic isn't doing so hot on the MPGs any more, for instance. In which case, it's time to start driving more efficiently with the car you have.
Follow simple tips to green your drive like lowering the A/C and rolling down the windows when you're in the city, and putting them up on the highway. Make more right hand turns—a seemingly strange but proven tip to rev up efficiency. Or use GPS systems to plan more efficient routes.
Point is, there are plenty of ways you can drive the car you've already got more efficiently. But the process starts with knowing what you're working with.