Coat the pan/pot with oil with a high smoke point. Every surface (except enamel) must be coated, the inside, the outside and the handle. It really has to be a nice thin layer, you can be generous with oiling, but then remove too much with a cloth.
Next, place the pan upside down (cooking cavity down) on the oven rack. Cover the oven tray with aluminum foil and slide it under the rack to catch any oil residue. You only now turn on the oven at 250 degrees.
When the oven is up to temperature, let it burn in for an hour at this temperature. I'm warning you now, this is going to smell like burnt oil. This is completely normal!
Let the pan cool in the oven with the door closed, until the oven is completely cold and the pan is also cold. Your seasoned pan is ready!