Splint the injury (see related eHows on splinting arm fractures).
Put a wad of clothing, or some other soft material, into the injured person's hand to maintain it in a functional position.
Gather at least two triangular bandages.
Orient one of the bandages so that the point opposite the long side of the triangle is pointing toward the same side of the injured person as the injured arm is on.
Keeping the elbow flexed at 90 degrees, position the arm so that the forearm is at a 30-degree angle to the ground, with the hand higher than the elbow.
Cradle the arm into the triangular bandage.
Pull the half of the bandage that is furthest from the injured person up and over the same side of the neck as the injury.
Pull the half of the bandage that is closer to the injured person up and over the opposite side of the neck from the injury.
Tie the two ends of the bandage together behind the neck.
Swathe the arm by first folding the other triangular bandage over several times: Start by folding the point opposite the long side so that it touches the long side.
Repeat folding in this direction until you have a long piece of cloth 3-4 inches wide.
Pull the bandage around the person: under the armpit opposite the injured arm on one side, over the injured arm on the other side. The bandage should be parallel to the ground.
Tie the ends of the bandage together.
Monitor the fingers of the injured arm regularly for circulation, sensation and motion.