Edmunds.com recently tested the most common "tips" you hear to save gas on your commute. Do they all work? Here are the results:

Test #1 Aggressive Driving vs. Moderate Driving Result: Major savings potential The Cold Hard Facts: Up to 37 percent savings, average savings of 31 percent Recommendation: Stop driving like a maniac.

Test #2 Lower Speeds Saves Gas
Result: Substantial savings on a long trip Cold Hard Facts: Up to 14 percent savings, average savings of 12 percent.
Recommendation: Drive the speed limit.

Test #3 Use Cruise Control Result: Surprisingly effective way to save gas Cold Hard Facts: Up to 14-percent savings, average savings of 7 percent
Recommendation: If you've got it, use it.
 
Test #4 A/C On, Windows Up vs. A/C Off, Windows Down Result: Nice in theory; not true in practice Cold Hard Facts: No measurable difference (unless you open the sunroof, too!)
Recommendation: Please, make yourself comfortable.

Test #5 Check Your Tire Pressure Result: Important for safety and to reduce tire wear Cold Hard Facts: No measurable effect on the vehicles we tested Recommendation: Check your tire pressure often but don't expect a big savings.
 
Test #6 Avoid Excessive Idling
Result: More important than we assumed Cold Hard Facts: Avoiding excessive idling can save up to 19 percent Recommendation: Stopping longer than a minute? Shut 'er down.