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

Learn the language, travel, if you're too young to drink, DON'T START!

Don’t go to the barbershops outside of post

Stay out of trouble

Get used to the cold....

Treat this as a PCS stateside and don't do anything, even innocently, wrong. Your tour of duty. You will be just fine.

PV2 (Join to see), the ROK is a great please with lots of sightseeing to do, like traveling by train from Seoul to Busan and experience the Pusan Perimeter. Visit historical sites to build your own Korean Culture Experience in the form of memoirs. Take a ride to the JSA and experience Korea in the aftermath of the Korean War. The quansan huts are still th here and still straddle the MDL. Visit the tree where the troops of CPT Bonifas were ambushed and hacked to death by security forces of the DPRK.

Don't eat the Kimchi for awhile ouch

I was stationed in Busan back in the early nineties. My recommend is:

(1) work hard and represent your country honorably as honor is a big thing in Korea.
(2) learn the language. It will make your tour there much more enjoyable and open opportunities that otherwise aren’t available to non-korean speaking service members.
(3) Enjoy yourself. You won’t regret it!

NEVER, EVER, EVER, let your dog out of your sight!!!!!!

#1 get you a regular passport you will have less issues should you need to leave the country in case of family emergency. I.e. the passing of a loved one. Not that it should slow you down much but it will help speed you up a lot. (Taking from first hand experience)

#2 go and buy you a nice camera and go sight seeing (if you can), because you can’t get drunk in the corner of a bar anywhere in the world, but you might not ever be in the same place twice.

That about all I can offer.