To end a thread, sew back through the last few rows or rounds of beadwork, following the thread path of the stitch and tying two or three half-hitch knots between beads as you go. Sew through a few beads after the last knot, and trim the thread.
To add a thread, sew into the beadwork several rows or rounds prior to the point where the last bead was added, leaving a short tail. Follow the thread path of the stitch, tying a few half-hitch knots between beads as you go, and exit where the last stitch ended. Trim the short tail.