Shift sooner. Keep it under 2000 until you get to cruising speed and the gearing won't allow you to go that low. When you're accelerating, go ahead and use the "poor" vacuum reading and keep the rpm low. (
Autospeed article explaining BSFC)
AC. Consider using it less. I live in Texas. I don't need it in the morning (with kids on board going to school). In the afternoon I wish mine weren't broken - I'll give you that one.
Coast in neutral - actively look for places where you can. There are a lot more than you'd think, once you start looking. The engine is idling at ~800 rpm instead of 2000+, so it uses less gas.
Oh, and I second and third the idea of getting a gauge. With calibration, they can be VERY accurate. And it will open your eyes as to what works and doesn't work for mileage. Minute-by-minute feedback is so much better than trying to guess from the fuel level.