The backing fabric should be at least eight (8) inches larger in both length and width than the quilt top.
If the backing is pieced, use 1/2" seams and press the seams open. Trim off selvage edges. Horizontal seams on larger backing fabrics work better with the longarm quilting process.
Make sure your backing fabric is squared up.
Press your backing fabric.
Use a safety pin to mark the top of the backing fabric is the print is directional.
Make sure the quilt top is well pressed.
Trim all hanging threads from the back and edge. Loose threads will show through lighter fabrics on the quilt.
To keep your quilt top as square as possible when applying borders-- be sure to measure through the top, middle and bottom of the quilt. Add these three numbers together and divide by three (3) to find the average. Cut your border to this length. This may require you to ease the quilt to fit the borders-- but helps keep the quilt top square.
Use a safety pin to identify the top of the quilt.