The thread you use for the applique depends on if you want it to show or not. To make it invisible use sewing thread the same color as the applique. If you want a more rustic country look use black thread and a blanket stitch. There are a variety of stitches you can use from a satin stitch to the blanket stitch. I use whatever stitch that will give me the look I want. If it is going to be an item that is washed frequently you might want to use a denser stitch. If for some reason you decide to use a metalic thread be sure and use an embroidery needle made for such thread or it will shred.