We use the same method for picking up stitches whether they are stitches on a neck opening or along a cardigan edge for a button band.
Using one needle (the size used for the body of the sweater), insert the needle one full stitch in from the neck edge. Wrap the yarn around the needle as in knitting.
Pull the loop through....
...to form a stitch on the needle.
Along a vertical edge of the neck opening you may not need to pick up every stitch, since there are more rows per inch than stitches
per inch.
After the stitches are picked up and you are ready to work the neck rib, change to a smaller or appropriate size needle.
