I do pull the bobbin thread up to the quilt top when starting to FMQ. Do I do it before I lower the feed dogs? Sometimes I do, sometimes I don't. After both threads are on the quilt top,I grasp the two threads and hold them away from the needle as I start to sew so I don't get them tangled up. Some people like to sew several small stitches in place and then trim the threads before FMQ. I like to leave my thread ends and knot and bury them later for a better anchor.