In the very rare case that your reserve parachute fails there are emergency tactics you can use to give yourself the best chance of surviving with the least amount of injuries.
The first thing to do if your reserve parachute fails is to spread your body out in an X formation. This increases the drag resistance from your body with the air slowing you down.
The second tactic you are going to want to utilize is to look for the softest areas to land. Typical areas that are softer to land on include snow, swamps and trees. This will be your best chance of surviving in an emergency situation. One common misconception that you will want to avoid is landing in water. Whatever you do avoid landing in the water as this will lower your chance of surviving.
You can lean towards the direction that you want to land, however while doing this you will want to make sure that you do not start spinning.
When you are close enough to the ground shift your body so that your toes will make contact with the ground first. Your legs will act as an important tool in absorbing the impact from the fall. During this step you will also want to hold the back of your head with your hands to protect your neck and skull.
After surviving the fall you will want to ensure that you are staying awake. Due to the shock, your heart rate will temporarily decrease, causing you to feel tired. It is extremely important to not fall asleep to give yourself the best chance of surviving the fall.