Measure the doorway width using a tape measure. If doors enclose the space, such as French doors separating a dining room from a living room, measure the clearance beneath the doors as well. Purchase a rug that fits within these dimensions.
Clean a bare floor using a damp mop and a cleaning product suited to the flooring material, or use water. Let the floor dry completely. If you are laying a rug over carpet, vacuum the carpet.
Cut strips of double-sided tape an inch shorter than the length of the rug.
Flip the rug over and strip one end of the protective backing off the tape. Apply the tape strips to the underside of the rug in rows about 6 inches apart.
Peel off the backing strip on the other side of the tape and flip over the rug to position it in the doorway. Press the rug with your open palms along its length to set the tape on the floor or carpet underneath.