Several frugality blogs have recently mentioned that shopping around for auto insurance can save you money, so I won't be redundant. I have learned a few other tips that could be helpful and will share those.
The first I've learned recently. My 'new' used car has a cool MPG calculator on it. When I bought it at 7,000 miles, the cumulative MPG average for the car was either 23.9 or 24 MPG. I've been fairly religious about using cruise control, even here in town. I've noticed on the 'instantaneous MPG calculator' that the real-time MPG usage improves by 20 to 25% when using cruise versus my foot on the accelerator. (I'm a scientist, so I did some trials to confirm my hypothesis!) I'm about to roll over 12,000 miles and my average MPG's have gone up to 24.3. I rarely exceed the posted speed limit on the highways and use cruise control a lot. Based on the 'fill-up' method of calculating MPG, I'm getting around 30 MPG on the interstate using cruise control. That tells me it can save gas, which saves money.
Another weird thing I do concerns route planning. I make a list of where I need to go on my trip around town, and then arrange my timing and route to do two things:
1. Make a one-way circuit so I'm not criss-crossing myself or re-driving the same road and
2. Drive the route so that I reduce or eliminate left turns at major intersections and when exiting parking lots.
Why is this frugal? Many car accidents and fender-benders occur during left turns across traffic. Fewer left turns in congested traffic reduce the potential for an expensive accident. A small bonus is that you don't sit at the light burning gas waiting for your left arrow. When using the 'right turn method,' you rarely wait (idling) a full cycle at any traffic light.
There are probably lots more ways to reduce your gas consumption and potential for every-day accidents. What's your favorite?