All I use is cast iron, and I must strongly disagree with the person telling you to boil anything in your skillet after cleaning it. Boiling water in your skillet will liquify any oil in the metal, and you'll just dump it all(the oil) out when you pour out the boiling water. This is why you should also never use hot water to clean your skillet. Once you have it properly seasoned, to clean it all you need to do are follow these steps -
1. Let it cool to room temp after you you are done using it. Cleaning while it is hot does the same thing as using hot water to clean with, or boiling water in it as previously mentioned.
2. Scrub the item with a stiff brush under cold water. If properly seasoned, then nothing should be stuck to your skillet unless you burned something in it. Cold water will not wash the oil out of the porous cast iron.
3. Wipe out any excess water, and heat the skillet on the stovetop until all the water has evaporated.
4. Wipe the skillet with an oil soaked paper towel while hot. The hot metal will draw in any oil that has cooked/burned out. You don't want any pools of oil, as these will harden up later and jut be a sticky/crusty annoyance. You want just enough oil to make the metal appear wet. Let cool and store.
If you ever get rust that you just can't get out of your skillet, then pour a coke in it, and let it sit in the oven with the light on. The light will create just enough heat to let the metal expand so the coke can work it's way through the metal. If you turn the heat on, then the sugar will carmelize, and then you have a near ruined skillet. Make sure you put a drip pan under the skillet when doing this, or else you'll have coke all over the bottom of your oven. After you do this will be the only time you should use hot soapy water to clean it, to get rid of any sugary coke left in the metal. Then just season again, and clean as directed above.