I always start my quilting in the center of the quilt and work towards the edges. With a strippy quilt I start with the stripe in the middle and work towards the top and the bottom. Next I quilt the stripes besides it.
When I have to quilt long diagonal lines (as background quilting) I also start in the middle of the quilt, go to the edges and finish off the thread there. I only turn when the lines are quite short, let's say 2 or 3 inches long. In my experience the fabric will become a little wavy when I don't keep that direction.
I think I have to mention that I do wholecloths and I don't quilt pieced tops - a plain fabric seems to "shift" a little more.