Find a point, aim at it, and sew towards it while you are looking at it. Pin, pin, pin. Even if you are not holding the quilt tightly, the pins are doing the job. I usually remove them as I quilt the quilt, but you shouldn't have to remove them until you have quilted an area. However, the great advantage over hand basting or tack basting with a gun is that you are able to move the pins if necessary before you cause a pleat or tuck.
Safety pins are definitely a good thing.
Use a light gentle touch. It will be much easier to quilt too. I just skipped doing this in a cable design and ended up with several way too fat when I was quilting away from myself and couldn't see the line. I tape the design to the surface and position the quilt over it and clamp it down with my big office clips to keep it from shifting. To get a mirror image of a design for the other half of a border, for instance, just flip over the design and shine the light through it.