city driving ,and stop & go traffic will kill your gas mileage.
1- you can make sure that the car is always in over drive ,the more the trans shifts the better fuel mileage.
2- turn the a/c off when not needed will be the best thing you can do for gas mileage in city , traffic, but it is summer time , so that could be tough to do.
3- if you are not using high octane gas , you should , but for those engine and how the pcm , a/f ratio is set up , you will spend less gas with premium, so you will save in long run .
4- every 2 fill ups , add like an fuel injector cleaner bottle to the tank and keep fuel system clean will help too .
5- and when you hit the 100k , definitely change the spark plugs