Select a book, magazine or online publication to read. Choose something that is slightly above your current reading level by skimming through the material. If you know almost all of the words that you see, it's too easy. If you know almost none of them, it's too difficult. Pick something in the middle. Choose a contemporary publication, as opposed to a 19th century classic or Shakespeare, to ensure that the words you learn are normally used in everyday conversation. Current newspapers are wonderful sources of modern word usages.
Read your selected material and identify new words you come across. Read the sentence in which the word appears and the sentences immediately before and after it to determine the word's context. You may be able to tell whether its connotation, or how the word makes you feel, is positive or negative. For example, if the sentence reads "Mary lay in a pool of shattered glass after she slipped and accidentally defenestrated herself," you probably can tell that the word "defenestrated" has a negative connotation. Make an educated guess about what the word means.
Look the word up in a dictionary to find its denotation, or actual meaning. If you look up the word "defenestrate," you will learn that it means "to throw oneself out a window," and now the original sentence makes much more sense. Form a mental picture that illustrates the definition of the word so that you will remember it when you hear the word. To remember the meaning of "defenestrate," you might think of the image of Mary lying on the ground, surrounded by shattered glass.
Use the new words you learn in conversation and in writing as often as possible to get used to saying them in proper context. Refer to a dictionary if you need help learning the correct pronunciation of the word.