Step 6: The edges
I use my sewing machine with a coloured thread in the bobbin and white thread in the needle, but you could use the same thread in both if you like. Sew with the plan white side down - this way you can see where your embellishments are and avoid them and they don't get caught in the feed dogs.
I like to use a zigzag with a wide stitch width and a short stitch length. Often I will go around the whole card twice, the second time with a slightly wider stitch to get good coverage. Letting the needle fall "off the edge" should ensure that the edge is completely enclosed.
If your machine doesn't zigzag, or doesn't play happily while you are doing this you can just edge stitch with a straight stitch close to the edge making sure you sew through all the layers. Again you may wish to do a second line of stitching just inside the first line for extra security. Alternatively you can bind the edge with ribbon - though I found this to be a fiddly process and it was hard to get a good looking result.
If you are sewing by hand use a new sharp needle and a thimble (helps to push through the fusible stuff and the interfacing) and do a buttonhole or blanket stitch around the edge.