What advice would you give to someone going to Korea (first duty station) who has never been out of the country before?

Enjoy it! I just got back from Korea. Have fun and don't get caught outside after 1 am. English is everywhere. Suwon is a good place too, but the base itself is small, from what I have heard. Go down to Osan or Camp Humphrey's. Travel. Don't stay alone in your room.

Its going to be VERY cold in the winter. Don't get an STD. Don't become an alcoholic.

The biggest thing I've heard for there from friends and people I work with/have meet is Korea is the fastest way back to a private you can get or the fastest way back to E-4 if your anything higher. In other words there are tons of things to do yes but it don't mean doing the wrong things. One thing to always keep in mind is the 4 questions you can ask yourself. The biggest two are am I willing to accept the consequences of my actions and is this morally/ethically right. Follow the basic rules and that includes any curfews.
Also as many have said don't go coming back with a wife. Yes sometimes it works but there is no guarantee. If you do meet someone special over there take your time. If its meant to be they will find a way to make it work with you no matter what. Also make sure that any relationships you do have whether long term or short you practice safe sex. You don't need another person or two to have to take care of cause of an oops in your life, take charge and make sure it doesn't have the chance to happen.
What MSG Dan Walther put out in his post I 100% agree with and is also a good set of guidelines to follow just about anywhere you go CONUS or OCONUS.
I don't have a ton of experience in the army but I have traveled a bit and some tings are, well, common sense if you want to keep yourself in good standing and want to move forward in your career.

Soju is awesome, but POWERFUL!

Enjoy yourself. See you in two months!