Pin pattern pieces to the fabric according to the pattern used. Cut the slipcover pieces from the fabric following the pattern outlines. Remove the pattern pieces. Indicate what each piece is by marking the pattern piece number or letter with chalk on the back of the fabric piece.
Place the cover's top piece on top of the bottom piece with the wrong side of the fabric facing up. The right sides of the print or fabric should be touching so that it is "inside out."
Pin the edges. Some slipcovers have strips that form the sides, front and back, called "gussets" or "welts." Gussets or welts make the slip cover or cushion three-dimensional or form a "box." Slipcovers with gussets used on sofa, cushions or chair cushions sometimes have a zipper or hook and loop closure at the back.
Sew the edges of the top and bottom slipcover pieces together, using a 1/2- to 1-inch seam allowance, depending on the pattern. When you near a corner, stop sewing about 1/2 inch away from the corner.
Turn the sewing machine wheel to manually "walk" the needle to the corner, stopping about 1/2 diagonal inch from the point of the corner, if using a 1-inch seam allowance, or 1/4 inch from the corner's point if using a 1/2-inch seam allowance.
Lower the needle into the fabric, using the sewing machine wheel.
Lift the pressure foot. Rotate the fabric in the direction of the next seam, but do not lift the needle from the fabric.
Lower the pressure foot. Sew the next seam. According to Elle Décor this pivots the seam, creating a square corner, reducing the likelihood of the seamstress curving the seam around the corner instead of creating a perfect 90-degree angle that fits the corner of the cushion of the sofa, chair, footstool or cushion being covered.
Turn the slipcover so the corner point faces you. Measure 1/4 inch from the point of the corner toward the seam. Upholster Magazine Online says to horizontally cut across the point, creating a flat edge. The edge will be diagonal across the corner.
Use scissors to snip 1/4 to 1/2 inch (1/4 inch if you used a 1/2 seam allowance or 1/2 inch if you used a 1 inch seam allowance on the slipcover seams) at the center of the point (now a flat diagonal edge) of the corner. Do not cut the stitched seam. This creates flexibility in the fabric corner and allows the slipcover to lie smoothly along the square angles instead of being pulled taut, puckering the slipcover at the corners.
Continue constructing and sewing the slipcover according to the pattern.