I will be visiting South Korea next month and need some help, any Koreans ready to help?

I will be visiting South Korea early next month for about a week. I would like to know if there is anything that i should know or prepare myself for. Especially in regards with clothes, hows the weather there? what type of clothes should i bring? how about customs, anything that is crucial that i should know about? any help is greatly appreciated. thanks in advance.