So here's some ideas that are "cheap" and relatively convenient. Short
of buying a $44,000 Toyota SUV Hybrid or something a bit extreme.

1) Use gasbuddy or some other website to try to find lowest price gas
in your area

2) Use a gas rebate credit card (preferably one with no fee). AAA has
a Visa card that gives you 5% back (based upon your monthly purchases).
Just be sure to check all the fine print (ie, sometimes Chase and
Discover only give you 5% for like the first X months).

3) Check your tire inflation and air/oil filters.

4) Accelerate a little slower. At least on my vehicle, it made about 2
mpg difference for a few extra seconds rather than flooring it to get up
to 60 mph quicker.

I'm sure others will have some other ideas as well.