Improving writing skill is a hard subject. I think there is no best way to improve the skill in short period of time. As indicated by many, it usually takes long time. However, it is generally said that a good reading skill accompanies a good writing skill. That means, you should have a critical reading skill, through which you can analyze and organize the idea presented in the material you read. In addition,by reading a lot, you can grasp various English expressions, which are different from the Korean expressions. That means you should give yourself a chance to understand the way of thinking of English speakers. Writing skill is not necessarily an ability to compose English sentences using proper English grammar, but a skill or an ability to present your idea in a commonly accepted essay writing manner. You can learn this from many sources. Taking a writing course will be a good option. But if it's not available, you can also find a book in which you can get abundant information on how to write effectively and efficiently. What I have been doing to improve my writing skill is to read daily newspapers and keep journal on any one of the topics in the newspaper of the day. When I keep journal, I try to paraphrase the article sentece by sentece using my own words, and compare them with the sentences in the original article. Well, why don't you give it a try!!