well only way your gonna get Gerard Butler abs is to put on some
serious mass... if you are very lean then the best you can do is flatten them babies out and make visible...
Best things for your abs are squats deadlifts, then behind those, some
Decline situps. I know you workout at home, so you might not have access to a decline seat for situps. picture hanging from monkey bars by your the back of your knees (PCLs) and doing a situp, that in my opinion is very good. and planks everyone here is big fan of the plank
Also weights, do all ab work with weights... I do my declines (when I do them) with 25 lb. plate... not much weight but its some!