This question should be moved to a discussion topic where you would get more answers, but I don't know how to do that. I would suggest that you try some of the novels written specifically to teach SAT vocabulary with words underlined and definitions available for words you don't know. You can find them at book stores if you just explain what you want. Also, some of the more difficult books such as the classics use vocabulary which requires you to look up words in the dictionary if you don't know them. Vocabulary books themselves such as the "Word Power Made Easy" suggested above do help. In addition, the real secret to improving vocabulary is to know the meanings of prefixes and suffixes which are added to the beginnings and endings of base words. Vocabulary is important to build anytime but especially before college.