Minecraft wiki entry for Shelters, associated text: Light up a large area with a grass floor. Then put two of the same kind of passive mobs (i.e., two pigs or two cows) inside. You can then breed them together and you can gather wool, leather, pork, beef and raw chicken safely. You might want to put trees inside so the animals feel more comfortable, or, if you're really ambitious, build a man-made forest.