Read challenging books that contain words whose definitions you don't know. Underline or highlight new words when you encounter them and find their definitions in a dictionary immediately upon seeing them. This is a fast way to pick up new words that does not involve formal memorization.
Copy definitions in long hand from a dictionary. The act of writing will help to reinforce your memory of a word's meaning. You can also type a definition repeatedly in a word processing program. Either strategy will put you on the fast track to remembering a word's definition.
Create vocabulary flash cards. These should feature the word on one side and the definition on the other. This allows you to study with these cards in two ways: you can either look at the word and ask yourself the definition, or look at the definition and ask yourself what word meets it. Combining these two methods of study will allow you to learn words and their meanings quickly.
Read books such as "Verbal Advantage: 10 Steps to a Powerful Vocabulary," "Painless Vocabulary" and "30 Days to a More Powerful Vocabulary." These works contain word lists and strategies for learning them as quickly as possible.
Make use of Internet vocabulary resources such as Virtual Salt's "1,062 Vocabulary Words" and Capital Community College's "Building a Better Vocabulary." You can also use a search engine to find many online vocabulary games and quizzes.