Apply fray repair glue to the edges of the rip to keep the fabric from becoming more damaged. Allow the glue to dry thoroughly before continuing.
Thread a needle with upholstery thread, which is thicker than normal seweing thread. Match the thread as closely as possible to the color of the couch so it blends in. Make the length of thread twice as long as the rip, so you'll have enough thread to fix the rip with tight stitches.
Begin stitching roughly half an inch under the actual rip. Stitch the rip using small, basic stitches, working side to side as tightly as possible. Pull the fabric together while you are stitching so the two edges meet.
Knot the end of the thread once the rip has been completely stitched. Scissor away excess thread as close to the sofa as possible so thread won't be visible easily.