Reduce air conditioner use


Air conditioner use can increase fuel consumption by up to 20%.  Source 


Use your vents to move air in the car.  Use sun shades to keep some of the sun off you.  If your car has a sun roof, close the shade.  If you are still too hot, at city speeds, it is more efficient to drive with your windows open than to use air conditioning.

It uses less fuel to control the temperature by turning the air conditioner on and off as needed than to run the air conditioner and turn up the heat a bit.