There's no way around it: to do well on the SAT Reading section, you'll need to have a fairly large vocabulary. Vocabulary is crucial for the Sentence Completion questions and for understanding the long and short passages.
Like or not, the best way to build a big vocabulary is to read a lot of books. Novels, poetry, books about science and politics and economics and philosophy, books you're assigned in school or stumble across in the library or steal from your friends' shelves. The good thing about reading is that it will enrich your life in a million ways that go far beyond the SAT. Books can break your heart, amaze you, and teach you how to live in a deeper and more meaningful way. I wouldn't be the person I am today if it weren't for the books I've read; David Foster Wallace, John Keats, Leo Tolstoy, Gabriel Garcia Marquez, Elizabeth Kolbert, and many others have shaped my personality and my outlook on the world.
But I assume you're reading this blog because you're trying to study for the SAT. The test is in a few months or a few weeks, and you don't have time to read your way through the library. You want to improve your vocabulary, fast.
Second to books, flashcards are the best way to expand your knowledge of words. But there's a right way to study with flashcards and a wrong way -- and studying the wrong way can cost you a lot of time.
Start with a basic list of words you want to know. The Reading Primer (found in the Powerscore Online Student Center available to students in our SAT courses) is a great place to start. Whatever you do, don't sit down with the list and start making flashcards. First, print out a paper copy. Then go through all of the words once, covering the answers with your hand. If you know the word on your first try, cross it off the list! Go through the new list again a few times, again covering the answers with your hand. There may be some words that seem "easy" or "obvious" once you've gotten a chance to glance at the answer. If you get them right several times in a row, cross them off the list too!
Now that you've eliminated the words you already know, you can start making flashcards. I prefer paper flashcards; I find that the physical act of writing helps me remember.
As you go through the flashcards, pay attention to the words you get right. Once you're able to remember the correct answer three or four times from a row, remove that card from the stack! Over the course of a few hours, you'll be able to whittle down your pile of cards to a small set of words that always trip you up. Maybe these are long words, or words that seem foreign or especially unfamiliar. You'll need to be creative to find ways to memorize them! I love using goofy images and other mnemoic devices. For instance, I always remember that "vapid" means "stupid or shallow" because "vapid" sounds like "vapor"; I always picture someone with nothing but air inside their head.
You can also write out silly sentences that use these words, or sing them to yourself in the shower, or challenge yourself to use them in your next essay or in a text message to your friends. As you conquer new words, your stack of flashcards should get smaller. But remember that you should be adding words too: if you get a question wrong during a practice test, add the vocabulary you didn't know to the stack. The same goes for unfamiliar words that you encounter during English class, in conversation, or while reading the news.
Remember that your hard work will pay off in a great score on the SAT reading. A good vocabulary will also yield big dividends in college! You'll have to face dense 100-page readings on sociology, literacy criticism, political science, history, and more, and you don't want to be reaching for the dictionary every two minutes. Plus, a good vocabulary allows you to call your enemies "obsequient miscreants with no sense of chivalry", and who doesn't want to be able to do that?