The easiest thing to do is to pop the roof rack off. It's drag pure & simple. If you're not using it, get it inside the car. Better still would be to leave it at home.
Skinny tires are another technique. They're lighter and have less surface area, so less drag and less friction (which also means less traction).
Whatever tires you have, keep them properly inflated, which here means at the high end of the rance printed on the tire carcass. Don't over inflate because that causes safety and wear issues. But under inflation kills mpgs.
Another thing to do is...and this kills me, too...drive slower. Do you remember 55 mph speed limits? These were a response to fuel shortages aimed at lowering the nation's fuel usage. The actual target speed was 45 mph, which is the point where aerodynamic drag starts increasing rapidly as speed increases. Steady driving at about 45 mph will get you best mileage. Seems like 60 MPH is another significant mark along the same curve. If you can't bear 45, try to keep it at 60 mph or below.
None of these will turn a 4M into a Prius or even a JSW, but you will get better mileage than you do now.