Love words. You have to really want to learn new vocabulary if you're going to succeed.
Look up words you don't know whenever you encounter them. After encountering and looking up a word several times, you should eventually be able to remember its definition.
Use a Thesaurus. A thesaurus is a great resource which enables you to know the more advanced equivalent of basic english words.
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 + logy = astrology .
Find a friend who speaks English. It's good to practise 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.
Listen to the radio, watch television, or find a podcast that you like in English, and practise understanding the language when spoken, too.