Step 1: Remove the peel from your large apple. It is ok to leave a bit at the top and bottom. Parents can use a small knife to carve out a face. Concentrate on the nose and mouth. Shrinkage will make them smaller. Ears are optional. With some practise you will get the hang of it.
Step 2: You will need to soak your carved apples in a "brine" solution to prevent browning. Fill a bowl with water, salt and lemon juice. Add your apples. Let soak for 24 hours.
Step 3: Next day, remove your apples from water solution. You can feed a string or wire through top to bottom of apple. Tie off at bottom. Allow enough string/wire to hang your apples to dry.
Step 4: Hang your apples in a dry location for a minimum of 2-3 weeks. Keep an eye on them to make sure the apples are not rotting. You can speed this process up a bit by placing your apples (without string/wire) in an oven on the lowest temperature for several hours. They will still need to dry out for at least a week outside the oven. Should you discover your apples are rotting, remove any mold with a cotton swab and use the oven-dry process to help prevent further rotting.
Step 5: Once your apples are completely dried and you are happy with the shrinkage you can now add some fun features. Whole cloves can be poked in the eye sockets for eyes. Grains of rice can be hot-glued in the mouth for teeth. If you like, you can add a bandana for a pirate look, an eye patch, fake hair, or a witches hat.
Note: Before you add hair, or hats you should seal your apple with a sealer. You can purchase aerosol craft sealers at craft stores. If you cannot find, you may also paint on a polyurethane or shellac. This will keep moisture from damaging your shrunken head.
That's it! Use your imagination and have fun.