We've got some modifications you can do here...
65+ Vehicle modifications for better fuel economy - EcoModder.com
And some tips here...
100+ Hypermiling / ecodriving tips & tactics for better mpg - EcoModder.com
But the utmost important is
real instrumentation. I prefer the Scan Gauge (which can be had here, for a discount) or the Ultra Gauge. I use both, and just for readouts, the UG is better- but for testing, and all around use, I love the SG.
When you have one of those, you can see what is better. For example, it may be better to keep in gear and DFCO than to use Neutral. You'll have to test and see!
