Like Mule Packer, my approach to my wok and cast iron is to leave 'em with a little grease/oil. They season up over time, I scrub them if I get an uneven spot, and they work fine.
When I buy a pan at auction I almost always take it down to the metal and start fresh. Here's what I do:
If you need to get it down to the metal again to re season, all the above will work but I'll offer one other option: Phosphoric acid. Phosphoric acid will take the finish off metal and if you have rust on anything it converts brown rust Fe203 to Fe2O4 (ferric phosphate). It's commonly sold (and recommended here for gun rust removal) as naval jelly, but you can get it at Home Depot as metal and concrete etcher for cheap in a gallon container. Put some in and swish it around a while, scrub a bit and it will get you down to the metal quickly, and the metal will be etched a little to hold the oil and give you a nice finish.
Oil wise put a thin coat on it, heat it to 400-500 on a grill as has been said (b/c you do not want to do this inside without a commercial grade hood), cook it off for an hour or so, let it cool, repeat several times.
"Seasoning" is just a polymerization of the oil. In the old days lard was so good b/c it polymerized well, though I've seen debate about this in modern times as the makeup of crisco isn't the same as old timey lard and even pig fat isn't quite the same as pigs now are fed a more grain based diet.
Probably the best oil to put on a finish is linseed oil or tung oil, but they're not edible so I wouldn't do it. I learned about them when I was restoring my home, linseed oil in particular can do amazing things and b/c it polymerizes well it would be great, but I'd worry about eating off it. An oil that is cheap, easy and edible that is still a good polymerizer is soybean oil. Flaxseed oil would also be a great choice, but it's a specialty item. Flax oil is the edible version of linseed oil, should polymerize great and give a good finish. I've just never bothered with it.
If you are getting uneven spots or it isn't holding my bet is either too much oil when seasoning it or the metal isn't good and clean for the initial mechanical bond. The Phosphoric acid will give you the good clean surface, then just use a thin wipe of oil and repeat the process a half dozen times and don't try to rush it.
Honestly the cast iron I've done hasn't been picky once I used the acid wash. I've used canola oil (moderate at best as a polymerizer) and cooked it off on the stove (I do have a commercial grade hood) and it has done fine. get that good first bond and you'll be fine IMO. I'm also not super picky about it, grandma's pans weren't perfectly smooth either.
Oh, after I scrub out with the acid I do neutralize it with a little baking or washing soda and rinse really well then heat it a bit to get it good and dry before applying oil, just not hot enough to burn me.