Here is a quick how-to for trimming a quilt that has been quilted to get it ready for binding.
Quilt that has been machine quilted
Rotary cutter, ruler, and mat
#1 Use your left hand to steady the ruler. Place your hand about midway on the ruler, as in not too close to your body and not too far away. Spread your fingers of your ruler hand out, placing your little finger on the outside edge of the ruler, using it as a stable fence.
#3 If you need to straighten the corner a little you can fudge…because the batting won’t show since it will be inside the binding. You can do this if your quilting gets pulled a little bit to the inside.
#4 Line up one of the lines on your ruler with the seam of your border. If your quilt doesn’t have a border, use the edge of the pieced blocks as your guide to line up the edge of your quilt to trim off the excess batting and backing. If you consistently line up your ruler, you will have straight sides and square corners on your trimmed quilt.
Safety note: Get in the habit of always closing the blade on your rotary cutter when you are not using it. Even close it between cuts. It doesn’t take any time at all to close it, but those little blade cuts you will get if you don’t close it will really slow you down!