CAUTION: NEVER put cold water in a hot pan! – it could warp or crack it.
Let it cool for a few minutes after cooking. Run the water in the tap until it is hot (or have a small pot of boiling water ready) then introduce it to the warm pan. DO NOT use any soap or detergent to clean it - that will degrade the seasoning and leave an unsavory residue. Soap should never be used to clean a seasoned pan because it will dissolve the formed protective barrier and embed itself into the pores of the metal where it will return to taint your next meal.
Put about 1 inch or so of hot water in the pan, just bring it to a simmer, then turn off heat. Let the pan soak for 8 to 10 min, dump out water and rinse with more hot water, then wipe it out with paper towels. If there are stubborn food residues use a clean plastic scouring pad (scrubbie) to scour the pan with warm water. Dry it carefully by placing over low heat for a minute.
Right before using it again wipe a little Crisco or spray a light coat of Pam on the cooking surface. Wipe off with a paper towel. This cleans and prepares the surface. Now add whatever fat or oil you are going to use for cooking.
Never start heating a cast iron pan on high! This can cause a hot spot and permanently warp the pan. Pre-heat with medium-low heat for a couple minutes. Or place the pan in your oven and set it at 350 degrees and let it preheat for 8 – 10 min. This is the best method for larger skillets (#10 and larger) and Dutch ovens. Then you can put it on the range burner and turn it up to medium-high (if you are searing meat.)
Use a stainless steel spatula (not chrome-plated steel) with a perfectly flat, smooth edge and rounded corners so as not to scratch the nice black layer you have made. A well-used one is ideal as it has its edges smoothed and rounded from use. Check those garage sales and thrift stores for one! If your spatula’s edge is not smooth use the fine side of a flat sharpening stone to hone the edge and remove any burr.