When putting beads onto your knits using thread, you have the choice to sew them on or to knot each bead. If you sew them only, more than one bead is likely to come undone if the thread is broken later on. To ensure that each bead stays in place you can choose to knot each bead. In this application, there is not an actual knot made, but the yarn is anchored with each bead.
How to knot each bead
Put your needle into the “knot” of a row on the outer edge as you would to begin the backstitch, but instead bring the needle out to the RS again, and into the loop created in the yarn. Tighten and repeat or complete the backstitch.
This method to knot each bead is more time consuming, but ultimately with make the beads more secure. Take care not to pull the thread too tight whenever sewing something to knitted fabric. Maintain the same flexibility that exists in the knitted fabric. Knotting the thread with each bead also helps keep the thread close to the fabric and more invisible.
Tools for adding beads
Use a dental floss threader instead of a beading needle if possible. Although the eye is very large on the dental floss threader (making it quite easy to thread!), it is smooth. A beading needle often has a grooved surface which can pull at the yarn. Use a longer length of thread to give more to hold into the enlarged eye of the dental floss threader. The other aid I suggest is to smear a very tiny bit of “okay to wash” fabric glue onto each place where you added beading thread. After the glue dries, cut the thread very close. I prefer the linked brand for flexibility. Use a toothpick to keep the quantity very small.