I begin my machine quilting line by taking one stitch, then pulling the bobbin thread to the front before taking 4-5 tiny stitches, then dialing to the regular stitch length.
I end the line of quilting by taking those same 4-5 tiny stitches, lifting the presser foot, moving the quilt out from under the needle 8-10", first cutting the bottom threads under the quilt, THEN cutting the threads on the front/top of the quilt AFTER I've given the bobbin thread a little tug to pull the last bobbin thread stitch thru to the top - it's just a little 'bump' feeling - and then cutting the front threads.
This seems to eliminate thread clumps on the back of the quilt for me.
Jan in VA