In order to expand vocabulary you should set a certain target. For example, two words a day. Of course, with time you can increase this number. You will need to keep a notebook (or a special file in your laptop) to write down the unfamiliar words you heard or read in the course of a day. Do not ignore the new words you come across in conversations with your family, friends and colleagues, in TV programs, radio, newspapers, textbooks, comics, novels and so on.