The best way to prevent flats is to make sure you install/fix it right the first time. Make sure you find the source of the puncture in the tread/sidewall of the tire. Inflate properly. Some people will probably tell you that expensive tires and/or tire liners are good flat deterrants, but I've had good luck with cheap tires from nashbar when installed properly sans liners. Note that no tire is "puncture proof." check some online dealers or your local bike shop for specific tires.