Everybody calm down he didn't say he wants to be less fat. He said he wants to look less fat. That is easy enough. All you have to do is go to a tanning salon and get them to spray tan on some abs and pecs. Problem solved.

On a serious not though if you really want to be less fat you have to consume less calories than you expend. Core training can be part of that but you also should eat less/eat cleaner and through in some HIIT. As for me in terms of core I do plyo-pushups, one arm pushups, pushups, crunches, v-ups, l-sits, and glute ham raises.