Learn a little of the language or have a phrase book handy at least, Koreans have very limited English (even at the touristy places) .

Go to Insadong! Visit the Insadong Markets for some excellent antique/souvenir shopping. Right across the street is the beautiful Gyeongbukgung Palace, and down the road is Changdeokgung Palace, with it's famous "Secret Garden".

spell it right first of all. its Seoul

Itaewon is a major tourist hangout and many flock to it for it's night scene, although Hongdae is a trendier. Insadong is the place to get gifts, also has lots of traditional restaurants. Check out a Korean Sauna (Jim Jill Bang) at least once. Cheap place to stay overnight as well, if you don't mind sleeping on the floor with many other people. Duc (Chicken) Galbi is a must, or Dwaegi (Pork) Galbi. Near city hall you can check out a traditional korean dance and music performance. Very interesting. SC banks allow you to use your foreign bank card. There everywhere.

Go to any of the city's many markets to absorb the local customs and culture.  Insadong is the perfect neighborhood for souvenir shopping, lunch and tea.  Take the Namsan cable car to get great views of the city and a family-friendly environment. And Biwon (aka The Secret Garden) is the best escape from the city life.  Go on Thursday if you want to stroll around on your own without a guide. 

Need some extra cash while you are there?? Check out worknplay.com temp jobs often available!!

Food is very good, Bibimbap is my favourite!
However be careful if you can't eat hot things and /or garlic.
Don't let the hotels suggest you anywhere to eat. All the other restaurants are much cheaper. Expect to pay about 10 € per dinner, including beverages :-)

Please stay at the Coex intercontinental hotel as it is by far the best hotel in the city.

I think things there are sort of expensive...
And you can find the tiniest tin of coke there...lol

clean, tidy but bit boring. Not many speak English