Gas Mileage

What kind of gas mileage does everyone get? I have only been getting about 13mpg which seems rather low. I use 92 octane gas and occasionally put fuel injector cleaner in it.

The other day a strange thing happened, when I turned the car on a plume of bluish/black smoke came out the exhaust, perhaps this is part of the cause. This only happened once though so I'm rather confused.

Oh yeah, my car is a 92 with 72,000 miles on it. Thanks everyone.