Does it ever seem like you hit every red light, particularly when you're running late? Maybe it's Murphy's Law; maybe you're exceeding the timing of the lights; maybe the problem is your attitude. If so, it's probably costing you gas money.
So take a deep breath, count to 10 and put something soothing on the radio; you need to get into the groove. Coast into stop lights and stop signs (braking kills kinetic energy, wasting fuel). When the light turns green, accelerate easily and smoothly, but not too slowly. Try ramping up from 0-50 mph (0-81 kph) in around 15 seconds [source: Allen].
While sitting still at a light or curb, turn off the engine. Unless it's below freezing outside, modern car engines don't need to warm up. So, depending on your idle rpms and whether your AC is running, your car can gulp down 0.64-1.15 gallons (2.4-4.4 liters) per hour while sitting still. By comparison, starting your engine only costs a few seconds' worth of gas [sources: Allen; Car Talk; Gaines and Levinson; GSA; Reed; Yetiv].
On the highway, kick in the cruise control to ensure you don't squander go-juice. Lock in your car's most efficient speed (typically between 45 and 55 mph, or 72 and 86 kph). If you really want to go for broke, try to make right turns only, even if it takes you out of your way. Package delivery companies have been known to employ this strategy, and it apparently saves enough idling time to make a difference [source: Allen; Car Talk; GSA; Wiesenfelder; Yetiv].