Keep an inventory of words you don't know. When reading books, magazines or newspapers, keep a pen and paper handy. Write down words you don't recognize or words whose meanings in the specific context confuse you.
Look words up in the dictionary. Consult the dictionary for definitions of words you do not understand. Read all of the definitions, taking care to try to understand the potentially subtle differences among definitions.
Use a thesaurus. A thesaurus will provide you with synonyms and antonyms for the word you have just looked up. A thesaurus will provide you with words that have similar meanings.
Look up any synonyms or antonyms you do not recognize in a dictionary.
Write sentences with your new words. Try to use every different meaning of the word to get a firm grasp on the differences among them.
Try to use one of your new words every day in verbal communication.