Measure the room to determine how much trim you need. Purchase trim no longer than 12 feet long. Any longer than 12 feet will increase the likelihood of the trim warping in the future.
Choose the style and type of baseboard trim you want. Baseboards come in finished stains like oak or mahogany, as well as unfinished. To save money buy unfinished and stain or paint them yourselves.
Cut shims to keep the trim off the floor. If you're having carpet installed, leave a 1/4-inch space underneath the baseboard trim. This allows the carpet to be properly installed and tucked under the trim.
Lay the trim along the wall to determine where seams will need to be cut. Use a miter saw to cut the necessary lengths of the baseboard trim. Cut all seams at a 45-degree angle.
Nail the baseboard trim to the wall using finishing nails. Nail these into the baseboard every 14 to 18 inches. Use a stud finder to ensure that you're driving the nails into wall studs for secure installation. Work clockwise around the room starting on the longest wall.
Fill the nail holes with a wood filler. After you nail all of the baseboard trim pieces to the wall, go back and use a wood filler to fill all the holes. Use a wood filler that matches the stain or paint color on your trim so you can't see the holes.