Wrap furniture with straight or wooden arms in a few layers of polyester batting before placing the slipcover on the furniture. Polyester batting or foam can also be used to plump sagging cushions. Use a nonskid rug pad instead of polyester batting for furniture made of leather or smooth material to keep the slipcover in place.
Drape the slipcover over the sofa. Position it so it is even on all sides, and also line up the base of the cover so it is even with the floor. The fabric should hang just above the floor surface, according to Home Furnish.com.
Tuck the slipcover fabric under the seat cushions so it fits the cushions tightly. Push rolled-up magazines kept together in large rubber bands or foam pool noodles down into the seat crevices to keep the slipcover in place.
Tuck in any excess fabric into the arm and side crevices of the sofa to create smooth lines. Fold under excess fabric at the top corners and on the arms of the furniture if applicable as per the size and shape of your sofa.