I hate adding more thread. It's right up there with finishing work; when I'm done knitting a sweater or stitching a bracelet, I want to wear it, not sew it together, weave in threads, add findings, etc. But, alas, adding thread and finishing work are almost always necessary in handwork.
There are a couple of ways to add thread to a project in progress. This post covers the technique that can be used in literally every project.
The most important rule is this: Always add a new length of thread BEFORE you end the old thread.
Why? Because in some stitches/projects, if you end your old thread first, you have no way of knowing where to start stitching again. In other words, use your old, short thread as a place marker. Don't end your old thread until your new thread is coming out of the same bead in the same direction as your old thread.
So, to anchor a new thread, begin by going through some beads some distance away from where your old thread is hanging. Pull the thread through the beads, leaving just a short tail (see Figure 1). In Figure 1 below, the old thread has a stop bead on it, and the thread is purple. The new thread I'm adding is yellow.
Using your needle, pick up a thread that’s in the ditch (or between connected beads) next to the bead where your thread is exiting (see Figure 2). Pull the thread, forming a small loop, and take the needle and thread through this loop to make a knot embedded in the beadwork (see Figure 3). This is just as if you were hand sewing or sewing on a button, etc.
Weave through some more beads (Figure 4) and make another knot. Make a total of three or four knots, always weaving through beads between knots, and always heading toward the bead your old thread is exiting.
Figure 5 shows the new, anchored exiting the same bead in the same direction as the old thread. Cut off the short tail left at the beginning of the anchoring (the one on the right in Figure 5). This photo pictures the real thread I added to the project; I didn't really want to stitch with yellow thread with this.
To end your old thread (which you can do as soon as your new thread is in place, or you can do it later), weave through beads and make little knots between the beads, just like you did to anchor your new thread. After making three or four knots, weave through a few more beads, and then trim the thread.