Welcome to the forums! If you haven't already seen this list, it's a good place to start:
https://ecomodder.com/forum/fuel-eco...ifications.php
Feel free to ask for help or clarifications. I spent a long time browsing this forum when I first discovered it, can't tell you how many hours I spent reading!
Sounds like you do pretty well with your car as-is. My advice would be to start a fuel log, and get yourself some sort of instrumentation---Scangauge, Ultragauge etc. The fuel log is a neat tool because it shows you how various changes to your vehicle affect your mileage.
It also shows you the effects of summer and winter months, as you can see the yearly dip in MPG when the weather turns cold (and here, rainy).
Outside of that, switching to synthetic oil is a good and easy mod, if you don't already use it. I waited until I found it on sale at Costco and bought boxes of the stuff, as well as watching sales on oil filters. My cost ended up being only about 10-15% higher than conventional oil, with the added benefits of longer oil change intervals and smoother operation.
Good luck to you, and have fun!