Purchase or borrow good tapes. Not only should they cover a breadth of vocabulary that you use on a regular basis, they should constitute strong teaching material. They should provide you with a definition of the vocabulary word, followed by sentences in which the word is used, allowing you to easily remember the word.
Create a study schedule for your tapes. You need to listen to your tapes on a regular basis, as with any other kind of studying. For instance, you could listen to your tapes every morning on the way to work, or every other evening when you go jogging.
Practice using your new words in everyday conversation. Make a conscious effort to assimilate the words into conversations with friends, until the words become part of your vocabulary.