The PSAT tests your ability to read critically. This includes the ability to use logic to understand sentence formation and the ability to analyze short passages. Using a practice exam, pay close attention to your ability to read short passages and then summarize the important facts. For example, see if you can identify the subject and themes of a passage, otherwise known as the subtext. Study PSAT vocabulary words and pay careful attention to the different parts of a sentence, like nouns, verbs, adverbs and adjectives.
The math section of the PSAT is comprehensive, so study the various math subjects you have tackled in high school such as algebra, geometry, graphs, unit conversion, percents and ratios and word problems. This way you are prepared for the different types of math you may be required to use. PSAT practice tests present you with a wide range of mathematical topics, so test yourself with a practice exam to reveal any problem areas you may have.
The PSAT uses multiple choice questions to test your writing ability. It does this by asking you to analyze sentences and paragraphs while looking for any errors in grammar or word choice -- if there are any at all. Since some sentences will not need any changes, study grammar and punctuation carefully so that you can be confident in your answers.
Since the PSAT is designed to predict your SAT scores, you are likely to excel in the same sections on both tests. If you are taking the PSAT for the second time, be sure to study for the areas in which you did not meet your goals -- if you scored well on a particular section before, you will likely reach a similar score again anyway. By studying your problem areas and gauging your improvement, you can determine how much studying before the real SAT might benefit you.