It is best for women to bring semi-casual wear. Short skirts are not recommended. Longer skirts are great, they look professional, and they are easier to use the "squatters" with.
Bring lots of makeup and tampons with you. It is much more expensive in Korea.
For safety purposes, it is handy knowing some US army or airforce men. They will help you in a time of need or trouble. Very good connections to have.
Bring a vibrator or other self-amusement toy. Most foreign men date Korean women, so many foreign women are lonely for a year. There is a saying "Men come to Asia for the women, and women come to Asia for the money." It is true!!!