When I need to re season a pan, I usually soak it in lye to strip it, then vinegar if it is rusty, then I dry it and coat it in avocado oil (grapeseed works good too, just don't use vegetable oil or butter). Then, open every window and disconnect the smoke detector and slowly (to not warp the pan) raise the temp until the oil starts smoking. Continue heating until the smoking from the bottom subsides as the shinyness of the oil disappears. Then, let the pan cool enough to add some more oil and fry potato slices. When they stick, scrape the pan with wood only. If the stuff sticks so bad that you cannot scrape it off without damaging the seasoning, get it hot enough to turn to carbon and repeat. Once or twice with the potato and nothing will stick, not even scrambled eggs.
Maintaining the pan is worth talking about too. Don't use soap. I've heard it a million times that the soap today no longer contains lye and that it can be used on cast iron, just don't. Use water only when washing the pan, if anything sticks, scrape off with wood, dry immediately with towel and lightly coat with oil and heat to drive off moisture. Wipe off excess oil and thats it. In my mind, the biggest misconception with cast iron care is that seasoning refers to the non-stick nature of the proper finish. That may be true, but it is only half the story. Seasoning is also something that tastes good, like a stovetop coffee pot that has never been washed. Seasoning = flavor, and soap strips that and leaves you with just enough seasoning to make you think it works that way.
When oil approaches it's smoke temperature, be aware that it will make its way into and onto surfaces around the kitchen you didn't think it could. If you have a good source of dust, the oil will rapidly become evident on the tops of stuff as a brown goo, even if it's near the ceiling or further from the stove. It is best to do that outside unless you enjoy cleaning often. I've seen what years of that built up can do in places people don't care.
Another option for stripping the pans if you don't like lye is using oven cleaner and putting the pan in a garbage bag overnight.