Basically, mastering vocabulary is about knowing and using words or phrases. As for words, it is estimated that educated native speakers know the meaning of at least 20 000 words while intermediate learners of English (B1-B2) know only 4 to 5 thousand words. Advanced students (C1-C2) achieve 8-10 thousand on average. In my experience, if your passive vocabulary roughly matches that of advanced learners', you can read books and watch movies and understand everything easily, but you will continue to encounter unknown words from time to time. International exams such as IELTS are designed specifically to check students' ability to deal with unknown vocabulary.
Pronunciation can be tricky, especially, if you don't have enough experience and haven't yet learnt common patterns. That's why I usually recommend to spend more time listening to authentic speech rather than reading texts. While reading, students tend to mispronounce certain words inside their heads. Listening, on the other hand, allows them to become accustomed to different accents and correct pronunciation early on.
One of the most advertised methods of learning vocabulary is watching TV shows. Proponents of this method often recommend using translated subtitles when you are new, then switch to English subtitles and after you reach advanced levels, disable them altogether. However, I personally wouldn't recommend newbies to watch TV-shows at all. If you enjoy it, that's OK but don't expect much in terms of return on investment in this case. Newbies lack basic vocabulary, which is also the most essential, so learning it should be their primary goal. When it comes to studying essential stuff, nothing really can beat vocabulary textbooks. At more advanced levels it may be beneficial to watch movies but again, you should stick to using English subtitles and carry out some analysis aftewards. This way, you won't miss common expressions, phrasal verbs and set phrases.
While vocabulary is absolutely essential to conveying information, grammar is not. Having said that, studying grammar can a great deal improve your efficiency. Over time several myths have emerged and I think this is the right time to debunk them.
Sometimes you may hear scary stories about students who've allegedly spent years learning grammar but still cannot communicate. To be honest, I have yet to meet those students because so far I haven't seen anyone who even remotely fits the description. Usually, students who can't communicate also lack grammar knowledge. Conversely, students who know both grammar and vocabulary are the most successful students who are able to speak fluently, write essays, read books and so on.
Probably even more frequently you may hear stories about those who suddenly started talking without knowing any grammar rules. This myth brings us to my first article on the importance of persistence and efficiency. Natives can do without deliberate grammar study, but this path is hardly efficient and is not worth following. English grammar is easy enough to master, so return on investment will be enormous.
Concrete suggestions on choosing grammar textbooks will be covered in future posts, but if you need to evaluate several options now, stick to the book that provides systematic view of grammar rather than gives an overview of numerous seemingly unrelated topics.
What is next
This concludes my third introductory article. These posts hopefully provide a great overview of the learning process in general without going into much detail. Next time I am going to summarize my thoughts in a Q&A post.