Quote Originally Posted by RGR
Great to be here, I am an experienced car modder (Mustangs)
and hope to get my Aveo up over 40 MPG full time. 36 MPG
before a broken timing belt. Please point me in the right direction
for first mods, etc!
An 11% boost shouldn't be hard to do.

First, get instrumentation so you have instant and trip average feedback (changing your driving habits is easiest & fastest way to gains).

Pump up the tires, make sure all the basic maintenance is done. Use the lightest weight synth gear & motor oil the car can take, particularly if you live where there's winter.

If you do mostly highway driving (guessing you do, from your 36mpg), aero mods are your best bet. All kinds of things you can do there to get more than 11%: Partial grille block, passenger mirror delete, smooth undertray, lowering and/or air dam, smooth wheel covers. More aggressive mods that require fabrication skills would be: rear fender skirts, and a kammback attachment on the hatchback to taper the airflow coming off the roof/sides.

Oh, and welcome to the forum.