Need Help in Buying Used Car

Hi,

I am new to this forum.
Nice to meet ya all.
First of all, I am a uni student.
And recently I decide to get a used car.
My budget is $3000-5000.
So, I am not sure what make of cars I should look for.
But what I know is,
I would like a high mpg to save on fuel, low mileage, and etc.

And also, give me some tips about what I should look for when buying a used car.(like oil, air filter?, and stuff)
I know about the carfax and stuff.

Thanks!