The other solutions work, but the easiest way to get this achievement is to use 2 controllers or play with someone else. When you get to the overhang where the skull is, have your partner or 2nd controller stand against the wall and jump on their head. Jump in the air, make the other player jump in the air right after you and then jump off their head one more time and you should be able to reach the skull. It is basically a triple jump.
If you are using an extra controller, just leave it alone until you get to the skull, make player2 kill himself and he it will respawn right next to you.