The simplest bed-sheet-to-slipcover method is to drape the sheet over the couch and tuck the material into the creases -- down the back and along the arms -- until the excess is just off the floor. But plunking on the seat, napping and otherwise getting comfy typically result in a bunched and messy effect. Hot glue can give the cover structure, and it nixes the need for needle and thread. However, if you choose the hot-glue method, not just any glue will do.
Choose Your Glue
Opt for washable, all-temperature hot glue designed for fabric -- slipcovers require at least occasional washes, so avoid standard hot glue, which will come loose in the washer. Using the right glue and a low-temperature gun, or one with a low-temperature setting, decreases the risk of burnt material.
Select a Sheet
A dark sheet, or one with a print, helps camouflage overall grime until wash day, while a white sheet offers cottage charm year round. A flat king-size sheet, allows for excess fabric, while a relatively high thread count -- 400 or up -- offers durability.
Lay the sheet over the couch, wrong side up -- check the hems' finished sides, if you aren't sure. Adjust it, so that it's neatly and evenly in place as a slipcover, but with the excess resting on the floor, not tucked in the arms' and back's creases.
Pick up the excess fabric, gathering it along the back of the seat, until it's barely off the floor at the front and back. Secure it neatly and evenly with straight pins. Do the same where the arms meet the seat, bringing the fabric at the sides just off the floor. The pins should be as close to the seat as possible, so that you can trim the gathered excess material.
Use scissors to trim the excess fabric, leaving a couple of inches for hemming. Bring the aligned cut edges together, folding them in even hems. Fix the hems together with hot glue. Allow the glue to cool before removing the pins and flipping the slipcover over, hiding the hems, and exposing the correct side.
Attach a wide ribbon along the bottom of the slipcover for a neat finish or as a dust ruffle, using hot glue. Pleat the ribbon as you work, if you like, and finish in the back to hide the seam. Gather the splayed excess material neatly at the couch corners.