If you already have plastic wrap and masking tape.
Step 1: Get all Materials together
Plastic Wrap - uh, any kind of plastic i think..
Electrical Tape - for parts where flexible tape is needed
Step 2: Line up the Roll
Each pass should cover the previous one by at least 2 inches i did it like 4 inches.
Also pay attention to how many you are going to need to make across so that you can space them accordingly.
Step 3: Tape end of roll
Step 4: Re-inforce tape with another tape
If your carpet is dirty or just hard to see the plastic you can put a piece of paper underneath and it might be easier.
Step 5: Put it on the wall
Make sure that you put it on straight and there should be no messed up edges on the plastic, if there are, spend some time to fix them.