Go and enjoy! I spent nearly six years living and working in Korea before meeting/marrying hubby and moving back to the U.S. and would still be on that side of the world if the U.S. Army hadn't seen fit to relocate us.
As far as dress, avoid anything strapless, avoid tank tops, and avoid anything with major cleavage. You'll see younger Korean women wearing all the above, but some of the older generation are still offended by bare shoulders. Shorts should be within a couple of inches of your knees, but skirts can be shorter without raising any eyebrows.
Do expect to garner some attention if you're outside Seoul. It won't be negative, but people may well be curious to see what the foreigner is eating, buying, etc. Also, if you visit a sauna while you're there (and they're worth a visit!), be forewarned that Korean culture doesn't have the same inhibitions about same-sex nudity that western culture does. Total strangers may try to scrub your back, wash your hair, etc. They're just trying to be friendly, and they'd do the same for/to another Korean.
When paying for goods or services, use two hands to extend the cash. Not a huge deal, but a common courtesy in that culture.
Oh, and if you find yourself on a standing-room only bus or subway, don't be surprised if someone with a seat tries to take whatever you may be holding --including child or purse. They're not trying to kidnap or steal. They're just trying to be helpful. :-)