When beginning a line of stitching, the ends of the top and bobbin threads sometimes form a 'bird's nest' under the fabric.  To prevent this, I stick a self-adhesive cirle of Velcro (the hook side) on the back of my sewing machine, directly behind the needle.  Before I begin to sew, I pull the threads across the Velcro.  The threads then stay secure and out of the way.  The Velcro on the back of the machine doesn't interfere with the fabric.