Tune Up?

So my car is giving me an average of about 17mpg i know it can do a bit better i already had a couple of people tell me to give it a tune up but honestly i'm not sure what they mean. I just recently changed out the plugs, plug wires, oil + filter, fuel filter, and cleaned my air filter am i missing anything else that might be causing the 17mpg? The check engine light is off and i am using 93 octane fuel.

Run fuel injector cleaner through a tank full the next time you fill up.

Should i use a specific one or any brand will do fine?

i used STP

Gumout brand is good.

Thanks

gumout is supposedly the best fuel system cleaner. Are you getting 17 mpg on the highway or the city? also remember that mpg can be greatly affected by the weight of your right foot.

For fuel injector cleaner I use Berryman B-12 (in the metal "old style" can/bottle).
You can also try changing your o2 sensor. The one before the cat.
Maybe tire pressure? Brakes dragging?

Well its mostly city but it isn't really much stop and go its mostly just stable 30-45... and id understand if i were the one driving it cause ill admit ive got a heavy foot but my mom had it for the past two weeks then again she might secretly be a speed nut lol... well i got the STP Complete Fuel System Cleaner so im gonna go ahead and give that a shot and see what happens and ill make sure and check the tire pressure as well as the brakes

It's rated at 18 in the city, so 17 isn't really something to worry about too much, I think.

Why do I get 13 in the winter

But yea, I wouldnt worry about your MPG at all if you drive throughout the city a lot, I think thats pretty good actually...

For whatever reason GPs get fairly respectable mileage on the highway, but crappy mileage in the city. But then again, considering the engine was originally designed in the 60's the highway mileage is probably remarkable lol

o2 sensor would be the other thing I would add to your list unless it has been changed within the last couple years.

Replace your PCV too. It's cheap and it helped my mpg when I replaced mine.

EDIT: Also make sure your tires are inflated correctly.