In order to reduce "back fat" or fat anywhere on your body for that matter, the most important thing is proper nutrition and a caloric deficit. If that is in place the the next most important is exercises to tone and strengthen these areas. For abs, bicycles and crunches are good. For your back, exercises like rows, lat pulldowns, chin ups, deadlifts are all good choices. Most women like to have pretty shoulders in a strapless dress also so exercises like shoulder presses and reverse flyes will help give a balanced look.
Remember, you can build those muscles all day long, but you'll never see them if you don't control the nutrition to remove the fat layer over top.