Sand the slippery area lightly with sandpaper. You do not want to remove whatever finish or varnish is in place, you just want to add a few microscopic scratches to create some traction in the treacherous area.
Apply anti-slip sprays that you can obtain from stores or online vendors that sell anti-slip products. Spray it over the affected area according to the manufacturer's instructions. This will provide a non-stick coating to your floor. Reapply it as needed since it will wear off with foot traffic.
Paint your floor with a friction paint. This paint includes small amounts of sand or other coarse objects to add traction to the floor. This is a short-term fix, since the paint will be scraped off by traffic around the house.
Apply traction tape to the afflicted area. This creates traction on the area but is only a temporary fix.