This link provides a few recommendations on how to prepare your hives for winter.
A few other items:
1) Make sure you remove the queen excluder between the brood chamber and any honey supers you leave on the hive. Although the worker bees may be able to pass through the excluder your valuable queen can not.
2) It is a good idea to fall feed ALL the new hives you started this year. These new hives are the most likely to have a shortage of winter stores.