Keep mitered corners aligned while gluing
Misalignment can botch any mitered corner. It's impossible to hide poor joinery here, so make sure you get it right by cutting several 4 x 4" blocks from a plastic laminate countertop. Clamp these blocks with their laminate toward the workpiece. The plastic resists the glue, and the blocks will hold the pieces in flush alignment.
—Richard Hopkins, St. Louis