Play vocabulary games. Scrabble is a popular favorite that utilizes its own special dictionary of compiled words. If your opponent drops the word "elt" on the board, your challenge may end with a small touch of irony. Many online and flash card games are also designed to enhance your vocabulary through fun. Crossword puzzles will also challenge your vocabulary inventory and stock a few extra words on your mental shelf.
Read, read, read. Develop a voracious appetite for reading and vary the types of books you read. Literary novels and other creative works can introduce you to new and imaginative words. A writer's job is to describe an imaginary reality on the pages you read. Writers will often employ a litany of tools in their linguistic arsenal to keep you turning the pages.
Study the dictionary, thesaurus and other educational vocabulary books. Scanning these reference books can introduce you to unfamiliar words and meanings as well as help with proper pronunciation. Learning the etymology of words can give you insightful background as to their origins and historical usage.
Engage in conversation. Everybody has their own level of vocabulary proficiency, and speaking with others frequently can open the door to vocabulary-building opportunities. Local colloquialisms and slang usage can be picked up simply by engaging in conversations with people. You never know what nuggets of casual vocabulary you'll be exposed to.