1. Look for water and build a shelter. Most people start by looking for food, but it is a fact that almost all "lost" people are found in a matter of hours or a couple days. You can live for 2 weeks without food but only 3-4 days without water.
2. Calm down. The most important thing is to remain calm and think clearly. If you start panicking, you can lose control and end up losing your chance of survival.
3. Evaluate your resources Do you have a source of fresh water? Do you have a long range radio, satellite phone, or other means of communication? Are there other people? People, if managed correctly, can be your greatest resource.
4. Act on all approved ideas together. Everyone in the group should work together to ensure that all needs are met, and to ensure that all resources available are put to good use.
5. Start a fire. This may seem like a trivial thing on a deserted island, but fire has a number of uses. At the very least, it is a morale booster. You have accomplished your first task, which is key for morale. Fire can also be used to distill water (more on that later), cook, and provide light for you and your rescuers. If you can't start a fire, don't worry, just move on to the next task and keep trying.
6. Build a shelter. A shelter provides a home base, somewhere warm and shady to sleep, a place for storing resources, and to hide from animals.
7. Look for water. Any source of water is good. As long as you have it, you can purify/desalinate it.
If fresh water is available, boil it for 2-3 minutes to be sure.
If you have a desalinazation device, great! If not, there are several methods to desalinate it.
One method is distillation. Construct a solar still, or one that works over a fire.
A solar still can be constructed by filling a large, flat container with salt water or even urine which can be re-usable, if need be.
8.Arrange rocks or large objects on a clear path to signal for help. The recognized mountain distress signals are based on groups of three (six in the UK). A distress signal can be 3 fires or piles of rocks in a triangle, three blasts on a whistle, or three flashes of a light, in succession followed by a one minute pause and repeated until a response is received. Three blasts or flashes is the appropriate response. If you are clear view of boats attempt to make a large red X.
9.Find food. Food is the lowest priority. The human body can last for weeks without food. There are lots of edible roots and berries, but watch out! Some are poisonous. Only eat them if you are sure they are safe. The best, and most reliable source of food is bugs. Yes, bugs. They are everywhere and an excellent source of protein. If deciding to fish with the bugs instead, a hook can be fashioned by carving out a stick into a hook shape and putting a barb on it. Tie string to it and you're in business.
10.Try to make contact. Build big, unnatural looking shapes using bright colors and shiny things. Use a radio, if available, to contact possible rescuers. Use signal mirrors, fires and flashlights and whatever else to draw attention to yourself.