Increase for shoulders:
Work to 1 st before first marker, pick up the stitch beneath the next stitch on the row and knit into it, k1 (keep marker before this stitch), pick up the stitch beneath the previous stitch (same st as you increased into previously) and knit into it, (2 sts increased). You can increase any way you like as long as you increase 2 sts in a line each row at each shoulder marker.
Work to next marker and pick up the stitch beneath the next stitch on the row and knit into it, slip marker, k1, pick up the stitch beneath the previous stitch (same st as you just increased into) and knit into it, (2 sts increased).
Your increase stitches should look like this:
Work the previous row increasing for shoulders in a line until the line along the increases equals your measurement from neck to shoulder plus 1 inch [2.5cm], or a little longer if you want more of a dropped shoulder.
You can take this opportunity to take it off the needles and try it on and see if you like the way it is going. It’s really not too late to frog it if you don’t like the fit.
I increased as described, for 11 rows, I started with 31 sts: 31 + 44 = 75 sts, distance from base of collar is 5.5 inches [14cm].