First things first, figure out which pieces you need to join together to be large enough for your quilt top.
To start, spread out two pieces of quilt batting on your cutting mat and slightly overlap the batting edges – roughly overlap ½ inch to 1 inch.
Using your quilting ruler and rotary cutter (or other cutting tool), place the ruler on the edges of the batting (middle of the overlap).
Set your sewing machine to a wide zig-zag stitch. Take your two pieces of batting and hold them against each other as you sew – this is where those straight edges come in handy!
Guide the strips through your machine slowly with the edges of batting butted up against each other. Take your time so you don’t end up with little gaps where the zig-zag stitch didn’t catch.