I usually use coconut oil. I have used flaxseed oil, but it's not worth the price. The secret is to rub it on a warmish pan, then wipe it off as much as possible. Put it in the oven upside down so any excess drips out,, set the oven to 450-500°, let cook for 10 minutes or so, then turn off the oven and let everything cool to room temp. before you open it. Then repeat the process. If you're restoring an old pan, look into using electrolysis with a 12v battery charger to clean it. The old timers would just throw it in a hot campfire and let it cool in the ashes.