Get several magazines. The heavier issues the better. Roll them up tightly, lengthwise.
Secure several rubber bands around the magazines. Hold the rolled-up magazine tightly while you put on the rubber bands.
Stuff the magazines down into the edges of the seat, going all the way around the seating in between the cushion and the back of the couch or chair.
Use a measuring tape to measure your seating area. Measure the entire seating area, length and width.
Take your scissors and cut a section of rug grip that will cover the cushions of your furniture. Rug grip can be purchased at your local home improvement store.
Lay the rug grip over the cushions and then place your slipcover over the furniture. The slipcover will be more difficult to get on the couch or chair this time because it will keep catching to the rug grip, so you will have to be patient and work slowly.
Use a measuring tape and measure the length of each of the sections around your cushion area.
Use a handsaw and cut thick dowel rod pieces, using your measurements.
Smooth out the slipcover and make it as tight as possible.
Insert the dowel rod pieces around the cushion, or in between the cushion and the back of the couch or chair, by placing the dowels rods on top of the slipcover and pushing them down. The size of the dowel rod you use will depend on how wide a space you have between the cushion and the back of the piece of furniture. You will know that you have the right size dowel rod when it fits snugly between the cushion and the back of the furniture, preventing the slipcover from sliding.