First: do you have fuel economy instrumentation? Like a ScanGauge or equivalent?
"Adjusting the nut behind the wheel" is the fastest & easiest modification that will save a significant amount of fuel. Do that first, then look at the vehicle mods. (Of course, not talking about maintenance items here.)
You will recover the cost of an MPG gauge in pretty short order. (And you could even sell it later once you've made habits out of your new efficient driving techniques.)
100+ Hypermiling Tips
Get the gauge, reset it to make each trip a "game" against yourself, use the tips that apply to your situation, and reap the rewards. Keep a fuel log to note your improvement.