4. Plan for hills
Even cars with good mileage ratings have a hard time getting the best gas mileage on hilly roads, so if your route runs through mountains or foothills, avoid using cruise control. Cruise-control systems in most cars accelerate too aggressively uphill, wasting gas, but don't allow you to save gas by coasting down the other side.
On the other hand, if your route crosses flat terrain, let the car cruise and give your lead foot a break. By doing so, you’ll use between 7 and 14 percent less gas.