Straight vocabulary is not tested on most standardized exams. In other words, you won't be expected to define difficult words. However, there are indirect and hidden vocabulary questions — of which you will probably find plenty.
Reading comprehension passages sometimes include vocabulary-in-context questions. These focus on particular words in the passage and ask you to determine their meaning. Sometimes these are "hard" words. More often they are seemingly "easy" words that are tricky because they have several possible meanings. The broader, more varied, and more accurate your vocabulary knowledge, the better your chances of answering questions quickly and correctly.
A solid vocabulary will also make it easier to get through the large amount of reading you must do on most standardized tests. Even an occasional math item is made a little more complicated by the use of a challenging vocabulary word.
Get into the habit of reading every day, with your dictionary and a notebook nearby. When you encounter a new word, look it up. Next, jot it down, along with its definition and the sentence in which you encountered it. Review your list periodically — say, once a week. Making the effort to write down the words and their meanings will help to fix them in your memory.
There are some topics for which you can easily cram. Vocabulary isn't one of them. Words generally stick in the mind not the first or second time you learn them but the fourth or fifth time. Try to start studying several weeks before the exam for 15-20 minutes a day. Periodically review all the words and quiz yourself, or have a friend quiz you. This simple regimen can help you learn several hundred new words.
Don't try to gobble dozens of words in one sitting. They're likely to blur into an indistinguishable mass. Instead, pick a reasonable quantity — say, 10-15 — and study them in some depth.
Language is a living thing. Words are the product of creative beings who twist, reshape, invent, and recombine them. (Think of the new language being created online, for example.) As a result, most words belong to families, in which related ideas are expressed through related words.
For example, the adjective anachronistic means "out of the proper time". Here’s an example of the word in context: The reference, in Shakespeare's Julius Caesar, to "the clock striking twelve" is anachronistic, since there were no striking timepieces in ancient Rome.
When you meet this word, you should also get to know related words. The noun anachronism means something that is out of its proper time. The clock in the above example is an anachronism; so are the pants worn by modern baseball players, which reflect a style that went out of date generations ago. When you learn the adjective, learn the noun (and/or verb) that goes with it at the same time.
The two words we just discussed are like brother and sister. Their origins can be traced back to the Greek word chronos, which means time. As you explore vocabulary, you'll find that many words come from Latin and Greek. As people in England and America imported words from Greek and Latin, they rarely imported just one from a given root. Thus, a root can help you to learn several words at once. In addition to anachronism and anachronistic, chronos is the source of the words chronic, chronicle, chronograph, chronology, and synchronize. All have to do with the concept of time.
Include the new words you're learning in your daily speech and writing. It will impress people (teachers, bosses, friends, enemies) and it will help solidify your memory of the words and their meanings. Maybe you've heard this about meeting new people: If you use a new acquaintance's name several times, you're likely never to forget it. The same is true with words: Use them, and you won't lose them.