The best way to save on fuel is to not use it at all - ride a bike, use mass transportation, etc. However, there is a rather large subset of the population that live in a suburban prison. The following is a set of techniques used by people that call themselves hypermilers to achieve high fuel economy/efficiency (FE) numbers, save the planet and save their wallets.
Step 1: Tires
Inflate your tires to, at least, the maximum inflation pressure to reduce rolling resistance.
Should you wish to go beyond, that is up to you. Personally, I inflate my tires to around 55psi (they are rated for 44). Please do not attempt on old or visibly damaged tires. My tires are new and in excellent condition.
Modern tires are radially belted - that is, they won't balloon like tires of yore. Keep in mind what you're doing though. You are reducing the contact patch of your tires in order to decrease static friction. This will reduce your overall braking ability. So riding someone's bumper at 80mph is just that much more dangerous. Again, these steps only work when combined - you can't pick and choose.
When it comes time to buy new tires, look for low rolling resistance (RR) tires. While they may not have the same 60,000 mile (or even 40,000) guarantee, they will save you in the fuel department. The Toyota Prius comes equipped with LRR tires.