Whip stitch is a good general seaming method that is often used to join afghan squares or to tack up a hem. The technique is very simple and fast. It involves running your yarn through the right half of a stitch along one edge and the left half of a stitch along the joining edge. The example shows a hem being sewn to the back of some purl fabric.
Insert the needle upwards through the back loop of one stitch and then through a purl stitch loop on the back of the fabric. Repeat for length of piece.