As a long time owner and a sometimes hyperiler(see signature), don't be fooled by all this talk of super high MPG numbers. People who are getting 90-110 MPG are doing it with some very special driving techniques. Those who can get 120 MPG are doing the "no holds barred sacrifice of all creature comfort routine, i.e. no A/C at at 90F, tires at 80psi, FASing a lot, driving very slow, etc. Frequently they are driving level ground and just brag about hot weather numbers (the car loves hot weather). In western Maine, you are suffering a handicap that others don't face - temperature. The best MPG numbers are set on hot days. On average, you have fewer of those than most owners. In most of the country, the difference between summer and winter is tremendous, so your generally cool weather is hurting you. Your winters are MPG killers!
When the car had a lifetime combined fuel economy of 53.6 it was actually .6 better than the EPA (53combined, 49 city, 61 highway), so the dealer didn't think there was anything wrong with the car!
Here are a few lessons I learned from others, in rough priority:
1. Nothing hypes MPG quicker than using a FAS circuit, shutting the engine off when opportunity arrises.
2. Slowing down helps. If in no hurry and under no pressure, 32 mpg in 5th has alway been a sweet spot. If you are trying to get somewhere, 52-54 in 5th is also a good spot.
3. Use high air pressures. 55-60psi is pretty common for folks who fixate on mpg. For competition, I have used 80psi.
4. As rainsux says, technique is very important. Try to use a "locked knee" stability on the accelerator. Keep an eye on the fuel consumption gauge. Try to drive so that it is as stable as possible and doesn't jump around.
5. Get in/stay in Lean Burn as much as possible. When in LB, try to stretch it as much as possible, even letting the car lose a couple of MPH on slight hills. The higher load you can maintain in LB, the better.
The best fuel is 87 octane, w/o alcohol if available. Direct comparisons to other cars compression ratio is a trap. The Insight head is designed for high compression on 87 octane. When you go to 93 octane you are substituting antiknock additives for the energy producing part of the gasoline. If you read widely on the subject, you will find this a uniform opinion.
+1 on everything rainsux says.
Get an OBDII C&C gauge so you have a positive indication of LB. It also has all sorts of other advantage which I leave to other threads.
After you have the gauge, go out on a good isolated, reasonably level stretch of road and practice. Find out what works and doesn't work. We have all fought this battle. When you get some of those 80-90F days you will get some number up where other hypermilers are residing