Preparing for the tests in advance is strongly recommended. The method and amount of prep can vary widely by student. Over the long haul, the best way to prepare is simply by reading. A Lot. Students should read anything they can that's written at a high level. We recommend a digital subscription to a newspaper such as the NY Times or Wall Street Journal. These publications are written at a very high level and offer a wide variety of content. High school students have a lot on their plate and most aren't able to commit to reading War and Peace, however, they should be able to regularly read fifteen minutes of whatever interests them in a newspaper.
There are many different test prep companies out there. Many of them offer a wide range of prep options. There are some free or low cost online options as well. The Khan Academy offers free SAT prep and does a great job of individualizing your preparation based on your PSAT results. Some students benefit from the structure of having a class once a week for an hour. Others are able to prepare just as well by sitting down twice a week and doing online or book prep on their own. We don't recommend one prep service over another. It's reasonable to take ease of schedule and price into consideration when choosing a test prep company. Here are a few of the companies our students have used in the past: Ace Tutor, Atlas, Huntington, Kaplan, Princeton Review, Sylvan Learning, Test Preps.