Put one ounce of household ammonia and one tablespoon of dish detergent in three ounces of water, and slosh the jewelery around in it for a bit. Don't let it sit too long. Replenish the entire mixture when it loses its strength. DO NOT USE WITH PEARLS OR OPALS.
An alternative is to buy a jewelery cleaning solution at a drugstore for about three bucks. They come with a neat little basket, a lid and everything. Then when it needs replacing, keep the container and basket and use the homemade solution in it.