Not having the pattern, I wasn't sure where you were. Usually the first dec is on a RS row, just so long as it's at the neck edge. According to the pattern you dec on 3 rows at the neck edge. Then skip the dec on 1 row and dec on the next row at the neck edge. And so on. The key is 'neck edge' that's the edge you want to be making the decs on. If you're at the armhole edge, you don't decrease there.
sue- knitting heretic