More of a sewing tutorial than a BJD tutorial, but it works for BJD clothes anyway. Someone requested this a long time ago and I can't remember who.
Sorry! Please let me know if it was you!!
Also, my mom pointed out in her customary proof-reading (she's much better than I am at sewing), if you sew too much on the snaps, they won't snap right. The thread will be in the way. So don't go overboard, but make sure it's secure.