Have you looked into the
65+ Vehicle mods? There are a few things on there that can definitely help. Unless the car already needs new springs, I wouldn't suggest lowering it, because the return on investment is very low. I'm not sure if the 2011 Accent already has one or not, but a smooth underbelly is probably one of the biggest aero mods that you can do without changing the look of your car. You could do a grill block and paint it so it isn't noticable, at a minimum completely block the upper grill portion. You could relocate your antenna to the inside or get a smaller (stubby) one or a sharkfin.
That should get you started down the right path, but before messing with aero modifications I'd say work on the way you drive and get yourself a Scangauge/MPGuino and/or a vacuum gauge. Driving techniques and proper monitoring will improve your MPG vastly more than any other modification you can do.
Edit: Also start tracking your mileage, it actually does help. Plus it lets yourself (and us) know how you're progressing.