Step 1: Scrape up your arm
This instructable utilizes a fine example of road rash on the ulnar side of the left forearm just below the elbow.
Step 2: Apply first-aid
If your injury is really manky and you have access to proper medical supplies, you may choose to use a more traditional bandage for the first day or two before moving on to the sock technique.
This injury was dressed with a proper first-aid kit at the site of the incident, thus the nasty tape-marks on the inside of the arm. After painful tape removal in the shower the next morning, we decided to bring out the sock.
Step 3: Acquire a clean sock
If you're a paranoid freak you could certainly boil, bleach, or otherwise sanitize your sock; of course, you're probalby not the sort of person to be making a sock bandage in the first place.