The better you do these steps, the better your quilt will be when you get it back:
The machine quilting process uses more backing fabric than front fabric so, your backing fabric should be larger than your top in all directions. For crib size quilts and smaller you will need at least two inches in one directions and three inches in the other. I can put your quilt on my machine sideways most of the time so it does not matter which direction is which for the extra inches. For larger quilts like throw quilts up to twin size we need two and four inches. For larger quilts like queen and king we need two and six inches. If you want the back to line up in a particular direction be sure to note which end is the top on both the backing and front fabrics.
Your quilt top and backing should be pressed so there are no pleats and the seams in the back are pressed to one side.. (Pleats often get quilted in permanently because I can not see the back while I am quilting.) Check to make sure all seams are sewn shut and pressed flat. Remove excess threads especially on lighter colored quilts as they tend to show through after quilting. Ideally your fabric will be square. Do your best to square things up. If you don't know how to do this, I can do it for you for a small charge.
Any seams that start at the edges of the quilt should be secure by either back-tacking the seam or by basting the perimeter of the quilt top to keep the edges from stretching while under tension on the machine. I can also do this for you for a small charge if you prefer.