Read books, newspapers and online articles to encounter new words.
Write down any words you do not understand, or are unsure of their meaning. Take a few moments to formulate an educated guess, based on context.
Reference unknown words in a dictionary and/or thesaurus. The dictionary will give you a fuller understanding of the word, and a thesaurus will grant you access to other similar words.
Write stories, articles or just ideas. Try to express your thoughts as precisely as you can, and use different wording. A thesaurus is invaluable for discovering new words with similar meanings.
Study prefixes and suffixes, which are common beginnings and endings of words. Knowing these can help your derive the meaning for unknown words. As an example, "uni" means "one;" if you already knew the "cycle" referred to a bicycle, then a "unicycle" could be guessed as having a single wheel. You might then break apart "bicycle" to discover by reason that "bi" must mean "two."
Some other common prefixes are "non," "anti" or "contra," which implies the opposite, such as nonbreakable meaning it is not breakable. Some common suffixes are "able," "ible," "ful" or "ulent," which implies the word is an adjective. Suffixes like "ence," "ance," "ment" or "hood" are used on nouns.