I have been studying Korean for almost thirty years, but not in a very systematic way. Also, when I started, there was no Internet, no personal computers, and few Korean language sources for foreign learners. In March 1977, when I first came to Korea in the navy, the best Korean language source for foreign learners were two books called "Myongdo Korean I & II." Later, a third and forth book came out, but they were not as good as the first two. These days there is almost too much out there.
I consider myself fluent, but there are different levels of fluency. For example, I can watch Korean soap operas, follow TV news, and discuss a range of topics with taxi drivers and others, but I still have trouble following certain discussions on TV and understanding groups of Koreans when they start talking in their abbreviated style of chatter, which is often filled with slang and idiomatic expressions. They also have background information on the topics that I do not, which makes it hard to follow them.
What are my suggestions for learning Korean?
First, I would get the 6-book series from the Yonsei Korean Language Institute and read through them about five or six times. Those books are filled with good stuff, and you will learn something new everytime you read them.
Second, while going through the Yonsei books, start with the first grade textbook on the Korean Lab Web site and work your way up. That will help make sure you learn the cultural items and language expressions that every Korean knows, instead of things that only a few super-educated Koreans know.
Third, get yourself a Korean chat friend because that will help you get plenty of exposure to the slang. By the way, here is a link to Korean Chat Expressions.
Fourth, stay curious and do not pretend to be more fluent than what you are, which means ask questions when you do not know. Read newspapers and college level material, but also read children's stories, which teach those little verbs, adjectives, and adverbs that foreign learners of Korean seem to have a lot of trouble with.
Fifth, learn the Korean idioms because they are used all the time. Here is a good Idiom Dictionary.
Sixth, learn Korean proverbs because if they come up in conversation and you do not know them, you will get lost. Korean proverbs are fun. Just read them at your leisure. Here is a Proverb Dictionary.
Seventh, learn Chinese characters and Chinese character idioms. Knowing Chinese characters will help you better understand and remember a lot of confusing Korean words. Naver has the best Chinese Character Dictionary I have seen. In fact, Naver has just about the best everything.
Eighth, listen to Korean news broadcasts. I listen to the KBS 9 O'clock News to develop my listening skills. After listening to the news on TV, I can go on the Internet an hour later and listen to it again while following a transcript the site provides. That allows me to see and hear the portions of the news that I did not hear the first time around.
Ninth, keep an online diary or write a blog in Korean. I do not do it, but I should. I do have this blog, however, and the reason I have it is that when I write about something dealing with the Korean language, it helps me to learn and remember what I am writing about.
Tenth, do not get frustrated. When you are nearing the top of one hill, expect to see another one on the other side. Enjoy the journey and do not worry about reaching your destination because there will always be another hill.
Well, that is my 10-Step Plan for learning Korean. I do not read many Korean novels or watch many Korean movies because both are a little difficult for me to understand and enjoy. I prefer TV soap operas to movies because the dialog is not usually mixed with background noise and special effects, making it hard to hear. Also, a soap opera is a story that continues over several months instead of just two hours, so I have time to follow the story, understand the characters, and learn their style of speech and favorite expressions.
I prefer reading Korean history and language books to novels because they have more explanation. I especially like Korean language related books. I also like Korean children's stories because they are fun and are stories that almost every Korean has read. Novels are usually too difficult and tend to mix in a lot of dialect, which I am not really interested in learning right now. There are too many things to learn, and novels seem to take up too much time.
That is how I study Korean, but I am sure everybody has his or her preferred way.