Prepare the Room
Remove all furniture from the room. Remove the baseboards from each wall with a flat pry bar and a hammer. Prepare the floors for carpet installation by sweeping the floors with a broom or by vacuuming the floors with a vacuum designed to work on floors other than carpet. Secure any loose flooring with nails.
Mop the floors according to the directions specified by your original manufacturer to avoid any damage just in case you later decide to go back to your original flooring. Check underneath the house to make sure you will not puncture anything like electrical wiring or heating and cooling ductwork during carpet installation. Mark any findings with chalk on the inside.
Measure the length of each floor corner with a tape measure and transfer the measurements to paper, using a pen. Cut the tackle strips with a utility knife, using those measurements. Place a strip on each floor corner with the pins facing the wall. Secure each strip with masonry nails and a hammer. Leave a 1/8-inch space between each strip and the wall so that you can join the strips at the corners.
Measure the length and width of the floors with the tape measure so that you can cut the carpet padding in strips that are long enough to reach the tackless strips. Lay the padding on the floor with the waffle side facing upward. Secure the padding with a staple gun and staples about every 6 inches. Cover the seams of the padding with some duct tape.
Install Used Carpet
Add about 4 inches to your measurements so that you will have excess carpet to keep from cutting the carpet too short once in place. Lay the carpet so that the pile faces the main doorway's direction and allow the carpet to overlap at least by 2 inches before cutting out the seams of the carpet.
Draw a chalk line, if needed, on the back of the carpet and then cut out, using a utility knife. Use this piece of overlay as a guide to cut out the other carpet pieces. Cut the seam tape the same length of the carpet seam. Pull the adhesive tape from the roll with the adhesive side up and center it under the carpet edges.
Heat the tape with the seaming iron and then press the carpet edges over the tape to secure. Place the knee kicker teeth into the carpet about 1 inch from the wall and kick the cushion end secure the carpet to the tackless strip you laid earlier. Repeat this step on all corners. Install a gripper edge to cover the carpet at the door frame so that the door does not damage the carpet.