bring bobbin thread to the top 3 or 4 stitches before you ran out- take a few small stitches to (lock the thread) before continuing with your quilting- snip off the tails.
some people recommend just a few stitches in place to lock stitches-
it helps to check your bobbin at the end of a line of quilting-on the edge to see if you have enough to make another pass...then you could change it at the edge before running out.