First and foremost, buying air tickets to Seoul do not entirely guarantee one's entrance. Nationals of some countries are required to obtain visas from South Korean embassies based on their homelands to legally enter. An appropriate visa would be granted, depending on the purpose of entry. Requirements should be submitted and legal 18moa procedures should be undertaken.
Before departure, travelers should also bear in mind that not all Koreans can speak English fluently. Rare times have it that some of them are even terrified of being talked to in that foreign language; although taxis have free interpreters; and signs have translations. So tourists should take time to learn even the basic phrases. Using simple greetings like "annyeong haseyo" (hello) and "kamsahamnida" (thank you) would be enough. For many locals, hearing foreigners speak their local language is enough to make them feel appreciated. So really, learning the language earns travelers plus points!
Another thing, people should also be updated with the weather conditions in South Korea before traveling. Spring falls between these months: March or April to May or June. Summer is from June or July until the month of August. Autumn is from either August or September to November or December. Winter follows from November/December to February/March.
It is important to know the season because that would tell which kinds of clothing people should bring. The cold seasons are literally cold, especially for people who live on tropical and subtropical nations. It is best to bring more thick clothes, coats, jackets, earmuffs and scarves when visiting during those times. South Korea hotels usually have heaters installed in their rooms so staying comfortable every night is guaranteed.
In terms of clothing, it is best to keep it toned down. Revealing clothes are also not to be worn in temples as this would just deny people entrances to these holy destinations. Although many Koreans are so much into fashion, they would not appreciate very revealing clothes in the streets. It is best to look casual all the time; yet keep that sophisticated vibe obvious.
These sums up the things that a traveler should bear in mind before going to South Korea. Remember that a travel adventure to this wonderful nation is surely worth the experience if one is prepared.