Been using an old Griswold cast iron skillet for ten or fifteen years now. It's what I make my breakfast with every day, and sometimes for pan roasting in the oven or searing a steak.
Once you have the primary season on it, maintaining it is simple. First of all, don't expose it to soap. Not even a little.
When you are done cooking, let it cool down to room temperature, then into the sink and pour hot water into it. Use a dish brush to brush off any bits that are sticking to the cooking surface. Pour out the hot water and rinse with cold water. Now wipe dry with a paper towel.
If you feel a slight slickness or oiliness on the cooking surface (you likely will), you are good for the next step. If not, apply a light coat of bacon grease to the cooking surface with a dry paper towel. Now put it on the stove top on high till it starts to smoke (one or two minutes, usually). As soon as it starts to smoke, turn off the heat source (It will continue to smoke a bit) and leave it there to cool down to room temperature. It's now ready to use again.
That smoking part is what adds the replacement layer of season (polymerized oil/fat) to the cooking surface, some of which you might have lost from using it last.
