I need to know how to work my core and strengthen it, I'm on the right track with everything else, but my core is weak and needs work. I have a flat stomach as well, but there's no muscle that shows unless I lay down, and right below my navel is this annoying, very light layer of flab I want to get rid of.

Bottom line, is I want my abs to show. I'm thin as hell, 130 at 5'9". Also where should I put the core exercises in my regiment? I generally do three days a week at the gym, chest day 1, back day 2 and shoulders as day 3.