The secret of seasoning is to get the oil (shortening) hot enough that it can melt into every single pore of the cast iron but not burn into a chunky hard mess. So, with your cookware completely coated you need to heat it up to about 300 degrees F and leave it there for an hour. This can be done in your oven, but it tends to smell pretty bad before the process is complete. You can also set it on some live coals. If it has a lid, put the lid on and put the coals on top of it. Remember where you want the temperature. One trick is to turn the pots and pans over and place foil on the rack beneath. This allows the excess oil to drain away and not burn on the inside of the pot. This too can be a messy proposition.
After an hour of heating, turn off the heat and let the cast iron cookware cool down where it is. You want this cooling to be nice and slow. Once cooled, you can remove it and give it another cleaning but this time just wash away any excess or burned on oil. Finally, take a few paper towels and some cooking oil and lightly coat the entire piece, store in a dry place.