Measure the length, width and depth of the drawer, container or shelf you intend to add dividers to with measuring tape. Write these measurements on a piece of paper.
Mark the measurements onto a sheet of plastic canvas with a felt-tip pen. The drawer's height will be taller than the height of the divider's sides. The drawer's length will be the divider's front-to-back length. The drawer's width will be used for you to calculate how many sections you want for the drawer and the width of each one.
Count the holes in each plastic-canvas section you have marked for the divider to ensure they match each other. For example, if one divider will have 15 holes from top to bottom, ensure the matching sides also have 15 holes.
Cut the sections from plastic canvas.
Thread a 20-inch piece of yarn into a large-eye needle. Knot one end of the yarn.
Hold two of the divider sides together at a perpendicular angle and insert the needle through the adjoining holes in the canvas pieces. Wrap yarn around the two pieces and place the needle back into the same hole to secure the sides -- forming a corner -- together.
Join the pieces together using a whipstitch technique. Stitch diagonally from one sidepiece, over the edge and into the next hole in the row on the second piece of canvas. Make three stitches in each corner hole to secure the pieces together.
Stitch the remaining sides and stitch on a bottom piece to the divider.