intercostals and serratus are the result of super heavy squats and deads, nothing else.
Abs, I've followed the same routine and only this routine for years. It was taught to me by a powerlifter who currently has a 900+lb competition squat. Anyway, you find a decline bench thats nice and steep. Slowly lower yourself down abuot 1/2 way, and hold there for a slow count of 5, then come back up. Thats one rep, for your first workout, aim for say 5 sets of 5 reps. If you hold the slow 5 count on each rep, trust me, that will be enough. When you can do that easily, either add weight or reps. Over the years I've built up to 5 sets of 10 reps with a 45lb plate.
Thats the whole ab routine guys