1998 Nissan Altima Decreased Gas Mileage

I recently moved my car overseas (The Middle East). Back in the states it was getting around 30 mpg. The gas here is different and I have little doubt that it is just plain lousy. The mpg on the car has decreased by almost 50%. I know part of the problem is city driving combined with heat but does anybody have any suggestions on how to improve the mpg, or better yet, how to preserve the engine in my car? I would like my car to last for a few more years.