It's almost all about what you eat, some ab exercises are helpful though. One i commonly do is I'll lay on the floor and rest my head underneath or beside the edge of a supported couch or table, then lift my knees up and back down and out straight. I feel it a lot on my abs and they have gotten more noticeable lately.
If you you really want to drop the fat try and eating foods that have little to no fat content, also maintaining protein is still helpful. I always eat Greek yogurt all the time, lean chicken certain canned tuna or even canned foods actually have practically no fat. I eat one quite often and it has 0.5 fat per can but don't eat too much canned anything due to sodium etc. Eat loads of vegetables and some kinds of fruits are good too.
around 1 month ago I went from around 11.5 BF to around 8.8 -9.4 by going on a 2 week cutting process. Lost around 6-8 lbs but it was mostly fat. There was a chart another RJer posted that was pretty accurate of how to have noticable ads. 10% - 12% for upper abs probably 7 - 9% for lower abs.
Anyways that's what I did, but look out for what some other guys mention, there's guys on here that have some pretty ridiculous cores.