Notes

Pour a small amount of the flax seed oil into the pan. Less is more with this stuff, so shoot for more than just a few drops, but no more than a tablespoon. Start with a teaspoon and go from there. Then, using a paper towel or rag, spread the oil evenly throughout all the surfaces of the pan, including the bottom of the pan, the sides, and even the handle.

The pan should have a slight sheen to it, but no standing puddles of oil or thick areas of build up. If you're really feeling inspired, use your bare hands to spread the oil around and envision yourself back in the old world. Follow the rule of thumb for any other finish - shoot for a nice thin even coat. You can always apply more, and, as you'll soon see, you will.

Place the oiled pan inside a 500F degree oven for 30 minutes. Some sources say to heat the pan for longer, but, if you've put on a thin coat of oil I've found that 30 minutes is plenty long enough.

The pan will smoke a bit during this process. That is completely fine and natural, your oven will not catch fire.
The hot flax seed oil will smell a bit strange. That is also completely fine and natural, the smell will go away.

PRESS ON!
Once you've "cooked" the pan for 30 minutes, remove it from the oven and let the pan sit until it's cool enough to touch. When you're sure it's not still hot, reapply a thin coat of oil using the same method described in step 2, put it back into the oven and cook it for another half an hour.

Keep repeating this process until you've gone through as many cycles as you'd like. I've found that 4 to 7 rounds was enough to result in a semi-gloss, beautifully smooth, tough, black finish that is ready for use.

Final tip - do all your cast iron pans at once. In my opinion, if you're gonna crank the oven up to 500F for several hours and make the house smell a little funny, you might as well make good use of it and season all your cast iron cookware at once. The good part is that you won't have to repeat the process very often. I've been going on the same seasoning session for several months now and they still look great.