What you want is flax seed oil. This stuff must be kept cold and must be used within a few weeks. I mean, mineral oil would be the best because it would give you a nice glassy layer, but it isn't exactly safe to consume...
So, flax seed oil is the next best thing. Give the entire pan a liberal coating... use a paper towel to make sure every spot is coated... heat the oven to 400 and put it in there for about 2 hours. Let it cool after and do this again... I would do it 4-7 times for a good coating. Also, the more you cook in it, the better it will be.
Do not use soap on it because that will break down the oil. Just clean with hot water... very hot water... and a scouring pad.
Don't forget to coat the bottom of the pan as well. That part can rust easily... Oh, and always dry it when done. I towel dry then use heat for the rest.
One thing I see rarely mentioned. Excluding the inherited cast iron that has been cooked with for decades, soap will typically damage/destroy the seasoning. Sea Salt/Rock salt with some crisco will NOT. The salt does not melt in oil and will scour away most any crud BUT you can damage the seasoning if you scrub!
I have multiple cast iron pans and this is the ONLY method I use.
i use salt and warm water to clean my cast iron, then i dry it and wipe it down with cooking oil, which ever i have, canoil or vegi oil or olive oil.. not concerned about rusting on a 30 dollar pan.
just remember, unlike cartoons, if you hit someone with a frying pan in real life they die and you go to jail and have happy shower time with garry. gtg garry's calling.