I hand quilt and about every 20 stitches I twist the needle and thread the opposite way it is twisting. This untwists the thread and prevents knotting. If that doesn't help, I clip about 1 inch off the end of the thread - sometimes the end gets a little frayed and causes knotting. I stopped using Americana thread because it was causing bearding and excessive knotting. I am now using a Guetterman hand quilting thread and it doesn't beard or knot as much.