The question of what MPG to expect is simple, but sadly almost impossible to answer in a way that really helps with anything.
The problem already starts with the "simple task" of measuring the used fuel. Filling up the gas tank all the way to the top is already not as easy and simple as it should be because of the shape of the gas tank and the pumps starting to shut of way before the tank is full. I can usually slowly fill almost 4 gallons into the tank after the pump at the gas station starts shutting off the first time.
Then there are also all the factors than impact MPG of any car such as the environment you drive in ( is it flat or hilly, cold or warm, in the country or downtown....)
Then it depends on the type of fuel you put into your tank.
And it also greatly depends on your personal driving style and how efficient you drive.
(I enjoy driving kind of quick and sporty, but on he other hand whenever possible, I for example look ahead and approach red traffic lights slowly. I slow my car down very early far before the light to roll up to the traffic light slower, in order to avoid bringing the car to a full stop. That way I can often keep it rolling do not have to accelerate all the way back up from a full stop. That saves fuel and gives me a speed advantage over any car standing still when the light turns green, and I can easily pass them after the light while they accelerate.)
I always monitor my MPG when I fill my tank up, by habit to keep an eye on my cars performance. It helps notice when something starts going bad.
The MPG I keep track of varies pretty considerably.
In the two and a half years since I have my car I've moved 4 times and the usual MPG I got out of my car always changed because I drove in different locations. I moved from living right in the middle of downtown to a suburb in the southside of the city over to a suburb on the west side and then another 10 miles further out onto an island, where I now do most of my smaller errands on foot and for anything else I have to take a highway and drive 10 miles. So my driving habits and with that the MPG I got out of it changed considerably whenever I moved, because I used my car very differently depending on where I was.
I always just get the cheap regular 87 octane fuel (but even that can actually vary in "quality" quite considerably and on occasions you can sometimes get lucky to receive higher grade fuel without knowing. On the other hand of course you can also end up being cheated on by a bad shop and fill your tank with a considerable amount of fancy $3 per gallon air bubbles in addition to the fuel.)
Anyways, that being said:
Downtown I used to get as low as 14 to 16 MPG sometimes less than 14, but I drove much less.
Now living on the island I get round 17 sometimes up to 19.
While working on my AC and letting the engine idle a lot I only got 12 MPG out of a full tank.
My best MPG on a longer trip, driving only on all flat highways through Florida with cruise control for days was over 20 MPG, almost 21 MPG.
