I anchor my quilt well with about 3 SITD rows each direction, depending on size. If I plan to ditch the whole thing then I might do more. When the quilt is that secure it doesn't matter where you start quilting it. I do as Harriet Hargrave said and start at an edge to the left of the machine. Keep going until you get to the middle and turn. A quilted roll is quite a bit smaller than one that has pins and more maneuverable.