Question on typical gas milage and possible problem(s) if low milage

I am a senior citizen and recieved this 1987 Nissan Maxima as a Xmas gift by my family.  The car was in great looking condition and has only 90,000 miles on it.  My problem is the gas mileage is only 10-12 miles per gallon.  Is this typical for this model, as I had hoped it would give a lot better milage.  If it is not typical, is there any problem solving anyone can suggest to diagnoise the problem.   I am not a mechanic and live on a social security (fixed income), but need the vehicle for appointments and part time work.  Thank you