The most frequent question I've got recently is how to learn English vocabulary efficiently. It seems many studious learners tend to grab as many words as possible within a very short period. However, the reality is that most of them end up giving up the words they've worked on, this is simply because the 'panacea' they've been looking for doesn't exist at all.
Personally speaking, the most efficient way to catch up with all the necessary words you haven't done is to read and listen as much as possible and even you may also speak those words to help you booster the vocabulary.
Good luck with your English study!