Starts and stops for machine quilting can be problematic. If you stitch too many times back and forth is it too obvious. If you stitch too many times in one place it makes a "tag" on the back. If you do too little, your stitching can come out.
This is what I have found works for me:
I go back and forth with a short stitch once or twice. Then, on the back I put just a touch of thread knot glue at the start or stop. I use a small, inexpensive paint brush to dap the knot glue on the threads. I have found this to work very well.
The thread knot glue I use is made by Dritz and it is called "Thread End Glue". I purchased it at Joanne's. I do not wash my fiber art pieces, so I can't tell you how the glue holds up if you put it in the washer. If you have trouble with starts and stops, you might give this a try.