Put a piece of scrap fabric in an embroidery hoop to practice the stab stitch before you begin the cushion. This gives you a chance to learn to make the stitch even and control the tension of the thread before using the stitch on the cushion.
Insert the needle through the front of the fabric, at a right angle to the fabric, and stab the needle all the way through the fabric, drawing the needle out of the fabric from the underside.
Push the needle back through the fabric from the underside of the fabric back to the front of the fabric, close to the point where you pushed it through. Make a stitch 1/8 inch or 1/4 inch long on the front of the fabric by stabbing the needle back through the fabric the desired distance. Practice making stitches the same size in a straight line until your stitches turn out even.
Center stretch canvas in an embroidery ring. Stab-stitch the desired pattern, working from the center outward. Alternatively, stab-stitch a border 1 inch from the edge of the fabric on the right side of one of the cushion panels.
Continue making stab stitches in the desired pattern, such as a simple design or a border, around the cushion's edge. The stab stitch technique creates a bold stitch. Focus on making the stitches all the same length and keeping them straight.
Sew the cushion together on three sides, 1/4 inch from the edges of the fabric, using a sewing machine; or sew it by hand with close stitches. Insert a cushion pad. Tuck the raw edges of the fabric inside the cushion on the fourth side. Use a slip stitch to close the fourth edge of your stab-stitched cushion, or use a stab stitch to complete a stab stitch border.