There are a few basic things you can do to improve your MPG.
Driving habbits are probably number 1. Stop the 'stop-and-go' rapid actions. When you see a red light ahead just let off the gas and coast, brake when you need, sometimes the light changes and you dont even have to brake. You can't do this if you are bumper-to-bumper in balls to the wall 'gotta get back to work' driving, that is wasteful - hasteful is wasteful. When thi light turns green, it is not the 1/4 mile dragstrip, gently apply acceleration and then let up some before you come to your intended speed, dont worry about the sportscar next to you that is leaving you behind ...
2. Low Rolling Resistance Tires (ie Goodyear "FuelSavers" - rated up to 50 psi)
3. Increase air pressure in Tires (try at least 38-44, unless you're vehicle handles poorly)
4. Improved air-flow air cleaner (ie K & M)
5. Full Synthetic motor oil (ie Mobil 1, Amsoil)
6. Full Synthetic transmission fluid (mobil1 , amsoil)
7. Moon covers over tire hubs to reduce air drag at speed (Can be bought or made, up to 1% mpg increase)
8. Fold the passenger RVM back on door (if yours does this) - you dont really need it as much as you do in city driving where it doesnt matter as much if it is folded out.
9. If you are in a hybrid vehicle, and don't have an EV button, adding one improved my MPG 10%~!!! (I do mostly city driving and the dang motor is running when I am rolling to a stop, being able to enter EV mode (if permissible) cuts the un-needed engine, but must be done with care (in conjunction with veiwing SG2) of the charge on the traction battery.
10. Use a guage like a 'scan guage' , yes its over $100, but i have saved over half-dozen people (from making a call for tow truck/AAA) by resetting their computers in cars/vans that overheated, some in dangerous intersections - You'll be able to monitor near instant mpg, and other temps and voltages that your , and you wont have to visit autozone to get your error codes read.
( I hope to add one or two more and pictures as time permits)
Step 1: Scan Guage
Though I realized most people are not technical, this 'tech tool' is pretty straightforward to implement.
There is an OBD port on cars made after 1995? and OBD2 on 98 and newer. This provides much detailed information and connects to a scanner like a scanguage. Having the cool tool to monitor all the variables
gives you motivation to change your driving habits and implement other changes which you can directly monitor the before and after.
If you buy from the source it will be over $100, if you buy from auction you can get it under $100 !!