If you have fallen down a cave, you need to know how to survive. I am Steve, and I am also your last hope. First, find a way out the cave. Stay in the daylight as you try to break stone and dirt to get out. Once you're out, you need wood. Find a tree, punch it, and earn the achievement "Getting Wood." Scrape the bark off the tree (put it in your crafting slot in your inventory), then put whats left together and make a crafting table.
Find more wood, then make a pick axe. Once you have done that, you must burrow down into the ground and make a home. Using a furnace, made from cobblestone, to smelt some raw wood to make charcoal. This material will allow you to light a torch to brighten up a room. Remember, light keeps the monsters away.
Stay in your house for the night and expand it. Once it's day, you will need to sacrifice a cow to the Minecraft heavens by killing it. You will be rewarded beef for food and leather for clothing. Using the cobblestone you obtained when you dug up your house to make better tools.
                Now is when you mine. Mine for ores, find iron, smelt it, and make better tools and armor. Uncover diamond deep below and use this material to make the best possible armor/weapons in this world.
                Now that you are geared and ready to survive, find civilization. Look in the plains or hills for a village of people to live with. They will most likely have a farm of fresh wheat that they will be happy to share. You will need to kill some sheep for wool to make a bed, then you can get a well deserved sleep, knowing that you have survived, and will (hopefully) live.
               Now is the time I, Steve, should go. Adventure and protect yourself. Put this book back were you have found it, so that the next person can live. Goodbye.