I'm a worrier, and a cheapskate, and a heat wimp. Add all those together and you've got someone who drives with the air conditioning on during warm weather, while she worries that she's wasting money by doing so.

I'm going to worry a lot less now, though, thanks to CNNMoney.com columnist Gerri Willis. In a recent article, she listed several gas-saving myths, and one of them was that air conditioning wastes gas. She explained: "According to Edmunds.com, the air conditioning compressor does pull power from the engine wasting some gas, but the effect is minimal in modern cars. On the other hand, driving with your windows down at high speeds can create an aerodynamic drag." Yay!

Here are some other things to know:

• How you drive can affect your ultimate fuel use more than your vehicle's miles-per-gallon rating. This was no surprise to me, especially after this past year, when I read how incorrect many mileage ratings are. Here's a summary, from BusinessWeek magazine: "On Jan. 12, the Environmental Protection Agency announced that it plans to change how it calculates fuel economy for new cars and trucks to more accurately reflect the real-world mileage experience of American drivers. The EPA increasingly has come under criticism for outdated procedures that overestimate mileage by as much as 50% in some cases. Consumers are likely to see lower, more accurate numbers on window stickers of 2008 models arriving in dealer showrooms in the fall of 2007." So the bottom line for us is that to reduce our mileage, it's good to lighten our pressure on the gas pedal and to avoid rapid starts and stops.
  
  
• Gas additives and other products that supposedly increase your mileage by up to 20% probably don't. In fact, they can sometimes even hurt your engine.
  
  
• It's rarely smart to use a higher-octane fuel than your vehicle needs. If your car needs an octane level of 87 or more, then splurging on 89 or 93 isn't likely to make much difference, except to your wallet.
  
  
• You can take some of the sting out of high gas prices by getting rebates on your gas purchases via credit card. (Learn more in "Make Big Bucks from Credit Cards.")

Here are some more articles of possible interest:

"Save Money on Gas" (One tip: Some discount retailers such as Costco (NASDAQ:COST) and Wal-Mart sell extra-cheap gas.)

"Make the Most of Rising Gas Prices" (Another tip: Consider hybrid vehicles such as the Toyota (NYSE:TM) Prius, the Honda (NYSE:HMC) Civic hybrid, the Ford (NYSE:F) Escape hybrid, GM's (NYSE:GM) Chevrolet Silverado hybrid, or the upcoming Nissan Altima hybrid.)

"Gas Prices Won't Go Down" (Get an opinion on whether companies such as Anadarko Petroleum (NYSE:APC) and Petrobras (NYSE:PBR) are fixing prices.)

And finally, if you're excited by the prospect of saving more of your hard-earned dollars, check out our brand-new financial newsletter, GreenLight -- it's packed with terrific ideas and guidance and is written by some of our smartest and wittiest writers and analysts.

Wal-Mart is an Inside Value recommendation, and Costco is a Stock Advisor selection.

Longtime Fool contributor Selena Maranjianowns shares of Costco and Wal-Mart. The Fool has an ironcladdisclosure policy.