Get one of the apps out there for mobile devices that tells you where the cheapest gas in your neck of the woods is. Here's a link to an article detailing some of them:

http://money.cnn.com/2014/12/29/technology/mobile/gas-price-apps/

When you find a station with a good price then fill-up the tank whenever possible. Resist the urge to second-guess where gas prices will be a few days from now when you'll need to top-off the tank unless you're a commodities broker in which case I can't imagine why you're here reading this.

By filling the tank you'll achieve what is called "dollar-cost averaging" and over time you'll achieve a savings without driving yourself (pun-intended) crazy and wasting time in line at the pump. Remember time is money. By topping-off whenever you get to half a tank you'll assure no frantic searches for a station when it's least convenient and you won't run the tank to bone dry which can up your chances of having fuel-pump problems down the road if that's your habit.

If you work outside the house or make regular visits to an area a bit out of your neighborhood then check the gas prices in that zipcode as well-- you never know-- sometimes you'll find a station with such good pricing that you should make it your habit to buy from them. For instance in my area there's a station run by Native American's on reservation lands and since they are exempt from certain taxes their gas can be as much as $ .30 cents cheaper per gallon on an everyday basis.