Use a Thesaurus. A thesaurus is a great resource which enables you to know the more advanced equivalent of basic english words.
There are many computer programs and websites that have ways of giving you a short "Word of the Day" list with new words every day. Try going to www.dictionary.com. Scroll down and click on "Get the Word of the Day e-mail". If you enter all of the required information, you will get a new e-mail every day with a word, its definition, and an example usage sentence.
Get a personalized Google homepage and click on "Add Content". Search for "word of the day" in the search box, and pick some of the content choices that you'd like to have on your homepage. The author recommends Merriam-Webster (www.m-w.com), Dictionary.com, and Wordsmith.org. When you log on to your homepage, there will be a list of new words every day.
Read. Read all genres of books. When you come across a word you don't know, read the sentences around the word and try to figure out what it means from the context. Check your guess with a dictionary. This doesn't mean you should start reading medical textbooks or other books with lots of new words on every page. Set aside time each day to sit down with your book. Enjoy yourself!
Play word games with friends. Try Boggle, Scrabble, or Catch-Phrase. There are so many great games out there to teach you new words. If a friend comes up with a word that you don't know, ask them what it means.
Use the words you learn when you're talking to people or writing letters or e-mail. Using your new vocabulary is not only fun, but a great way to remember all these new words. Try to use at least three new words a day when communicating with anyone.
Learn roots, prefixes, and suffixes. Many words in the English language come from Latin or Greek words. When you combine these Latin or Greek words, you get new words in English. For example: astro ("astron" meaning "star") + logy (logos meaning "speech") = astrology (meaning "telling of the stars"). Buy an etymological dictionary (meaning "a dictionary of word origins").
If you learn any romance language (eg: French, Spanish, Italian), or Latin or Ancient Greek, these will help you immensely with improving your vocabulary, especially the two ancient languages here because so many complicated English words are derived from words that are simple and commonly used in them.
Find a friend who speaks English. It's good to practice using your new words. With a web connection, your conversation partner does not need to live near you. You can email, chat, and even phone each other using your computers. A friend who understands that you are learning can help you practice, use new words in your conversations, and offer you advice. Since talking to a friend is fun, it won't feel like work! If your friend wants to learn your language, too, it will be easier for both of you to understand each other's mistakes.