The 2000 most common English words cover around 75-78% of modern English used today and therefore vocabulary should be prioritised by frequency or by importance to your own needs. Knowing this much vocabulary will allow you to function in English, however what does it mean to know a word? Knowing a word means you understand deeply its form, meaning and use. This means you need to know which form of the word family to use in different situations, what the word itself means in different situations, and in what situations you can or can’t use the word in. 

If this vocabulary test shows that you have not mastered the high frequency vocabulary (roughly 2,000 words), then this will be your first step. Following this it would be a good idea to move on to learning the academic vocabulary of which there are around 500-600 word families that are very useful for academic use (i.e. for university study).