There are many beliefs about the way drivers handle their cars, but oftentimes they're wrong, especially when it comes to saving gas (and in turn, saving money).
First up, is the idle vs. off theory: according to MSN, people believe starting their engine uses more gas than idling. This is false - idling for an hour can cost you up to a half-gallon of fuel. Unless you're stuck in traffic, the news source states, turn off the car when stopped.
The second myth is that cars need to be warmed up before being driven. While this helps owners stay warm in their own car, it doesn't save gas. If you're ready to drive and the car is on... it's good to go.
As a vehicle ages, the fuel economy does not decrease. There's a caveat, however. "As long as it's maintained, a 10- or 15-year-old car should have like-new mileage," states MSN Autos. "The key thing is maintenance: An out-of-tune car will definitely start to decline mileage-wise."
Lastly, premium gas doesn't make your car go further... it's only used by specific cars, so avoid it unless your manual says it only takes premium.