How did you learn words in Japanese? By gradually being introduced to them *in context* right? The process is no different in the case of learning a foreign language. So take every opportunity that you can to read English and listen to English. When you first come across (see or encounter) a new word, try to work out what it means from the context.. If that doesn't work try to see if there might be a shorter word that you already know within the longer word - for example, you might know the verb "to deter," but not the noun "deterrence." Only after trying these tactics should you look the word up in a dictionary. After you've looked the word up, write it down - but in a full sentence, so that it is recorded *in context*. If you have the opportunity to speak with an English speaker, then try to use newly learned words, in context, during conversations. It is rarely useful to write lists of words on their own.