1) Don't waste the money on the high octane crap! Most newer cars (within 10-15 yrs) don't need it! read the owners manual and most will recommend 87 octane. I know there are going to be some that say that my car runs bad with anything less than high grade gas, well that is because you have started using high grade from the start and probably burned plugs and sensors, so now that is all it will use. Amazes me the amount of dealers that "recommend" high octane gas, it is in the owners manual what your vehicle needs.
If you DO need to use high octane gas, by a can of octane boost (around $2) and add it to a tank of "low grade gas"
At prices now will save you about $5 a fill up!
2) don't use the air conditioner if possible (belive CraigL mentioned this)
3) don't accelerate quickly, or avoid stopping fast, you see a traffic light that you think has been green awhile let off the gas and be prepared to stop.
4) Use cruise control (or auto pilot

5) Watch your speed, going over the limit might get you there a minute earlier, but the extra fuel you burn isn't worth it, otherwise if you need to be somewhere leave the house earlier

4) No street racing, beyond popular belife, those little "chainsaw sounding" 2F2F cars look rediculious. If you must show off to your buddies and waste gas buy a '69 GTO! ;D
5) Don't come to Sevierville, TN!!! You'll burn a tank of gas just trying to get a 1/4 mile down the road! The South has yet to figure out how to time traffic lights

Hope these help