A poultry brine can be as fancy as you'd like, but the basic ratio is the following:
1 cup sea salt
1/2 cup sugar
4 quarts water
I usually boil 2 quarts of water , dissolve the salt and sugar and then add 2 quarts of ice water. This will bring the temperature down quickly so you don't have to sit around waiting for your brine to cool before putting your bird in the water. You want the brine to cool to below 41 degrees prior to placing your cold chicken into it. If your chicken is frozen you can thaw it in a brine, but the brine should still be below 41 degrees. If you would like a more flavorful brine you can use your salty-sugary boiling water to make a tea with anything from lemons and thyme to garlic and celery.
Brining times vary according to the size of your bird:
up to 2 lbs: 6-12 hours
2-5 lbs: 12-24 hours
5-10 lbs: 24-36 hours
10-20 lbs: up to 48 hours
A few notes, dr. Bronner style:
Never reuse your brine! Always use a non-reactive container! Be sure the bird is fully submerged! Refrigerate your brine! Let your bird air-dry for crispy skin!