Hi! I would recomend Talktomeinkorean.com for grammar, though the vocabulary is not very good. Memerise is a very good place to learn vocabulary, and I recomend it highly. You also may want to use TOPIC vocabulary lists, and online courses. Beautiful Korean also is very helpful for learning slang terms, while simply looking up'informal Korean speech' will help you learn how to speak with someone your age or younger! Last, but not least, I would recomend asking lots of questions and speaking to native speakers;)