If you teach your self Korean, you should get a proper textbook. Though there are many textbooks for learning Korean, I would like to recommend this textbook for the novice. 맞춤 한국어1~6 영어권(for English-speaker), published by 재외동포교육진흥재단(The Educational Foundation for Korean Abroad) you can download textbooks(Ebook, PDF) from following link. http://www.efka.or.kr/user/info/data.asp?page=2&sText=&search=&bbsName=&leftNum=

You might want to practice common phrases - hello, good night, nice to meet you, my name is... Now that you can read Hangul, your pronunciation will improve greatly if you keep practicing speaking or reading out loud. Learn nouns and verbs, because even without knowing grammar, you can get lots of meaning from knowing the context.

I would say sentence structure (verb at end) and conjugation of adjectives/verbs.