Seaming Shoulders?

Help! My sweater pattern just say “join shoulder seams”. The shoulders were bound off, otherwise I’d do a three needle bind off. Is the mattress stitch my best bet? do I do it right sides together or wrong sides together? Thanks!

The “best way” depends upon the yarn you used and the style of the sweater. If it’s a lightweight yarn, mattress stitch is fine. You do it with the right sides butted up against each other (at least I do).

But mattress stitch, while neat and almost invisible, doesn’t give the seam much support. If your yarn is worsted weight or heavier, you might be better off crocheting the edges together (right sides together) or backstitching them. The trade-off: more bulk, but a firmer, more stable seam.

How do I do the backstitck?

Here’s how.
http://www.hiraeth.com/ytg/texguide/backstitch/backstitch.htm

Most knitting reference books also have directions.
(Vogue Knitting, page 101; Knitter’s Handbook, page 249.)

If your yarn is thick, use a lighter-weight yarn in a similar color.