This is a bit of a grab bag of info. These are general tips for MPG, and things I've noticed that give me better gas mileage. Things I do have a plus sign for the bullets.
+ Keep the RPM around or below 2200. Slow acceleration is a huge factor for getting better gas mileage.
+ Half a can of Seafoam in the gas tank (with a full tank) and half in the intake manifold. I've gained 1.4 MPG by doing this.
+ Keep the speed 55 and below if you can help it. I've found that going faster than that frequently increases fuel consumption.
+ Use cruise control when the conditions are conducive to using it. This cuts down on RPM spikes when accelerating.
+ Don't idle. If you don't have to sit and idle, don't do it. It's just money that goes down the drain and idling obviously won't get you anywhere.
- Don't carry around excessive weight. The gas mileage tips page on http://www.fueleconomy.gov/feg/drivehabits.shtml
shows that 100 pounds of extra weight can reduce MPG up to 2%.
- Air pressure in your tires should be kept to what the manufacturer recommends. http://www.fueleconomy.gov/feg/maintain.shtml
states that tires under-inflated by 1 pound can cause a .3% drop in MPG. Properly inflated tires are also safer and last longer, saving you even more money in the long run.
- Use the right type of oil. Using 10w-30 in a vehicle that recommends 5w-30 can reduce MPG by 1-2%.
+ Clean air filters. A clean air filter (I change mine every time I do an oil change) will help with MPG. When mine's dirty, I've noticed a decrease of about 3/4 of a mile per gallon.
- Use overdrive gears (if your vehicle is equipped with such). Using OD reduces engine speed and also reduces engine wear.
- An obvious tip is to never drive more than is necessary. With the cost of fuel going nowhere but up, it's costly to take the long route to your destination, and even just taking that leisurely Sunday afternoon drive costs more money than it's worth. If you're driving to an unfamiliar location with the aid of a GPS, there's usually settings that can be changed to give you the shortest route (by distance) or fastest route (by speed) to your destination. Both of these, and your knowledge of the conditions on those routes can help with fuel consumption as well.
- When driving a lifted truck/ Jeep, making sure your rear axle has the right gearing can help gas mileage, too. Too low of gearing will require more acceleration in order to get up to speed. Higher RPM's = less miles to the gallon.
Hope this helps you get the most out of your gas mileage.