1. The best chairs for home re-upholstery are the kind with pop-out cushions (you'll see screws and/or nails underneath it, holding it in place). Unfasten the cushion and strip the old fabric and padding away until you're left with the cushion's wooden base.
2. Cover the base in cotton batting (pick up one or two yards at any fabric store), leaving three to four extra inches on all sides. For a cushier cushion, use another layer of batting or add a layer of one-inch foam. Staple batting all around the bottom of the wood with a staple gun-staples should be fairly close together and lateral, so everything is securely fastened. Trim excess.
3. Fabric can make or break your chair, so choose carefully! Get a yard of something heavy enough to withstand people sitting on it, like upholstery-weight brocade or velvet. Pull fabric taut over cushion (if your fabric is patterned, make sure it's centered!), then staple underneath. Trim excess.
4. Pop the cushion back into the chair and reattach. Now, sit down and enjoy!