Buy a book about the Mechanical Aptitude and Spatial Relations Test from a bookstore, or order it online through a company like Amazon. Look for a book that explains the test, gives you an idea of its format and provides you with sample questions. Read the book cover to cover, and complete any sample questions or tests the book offers.
Take a free online mechanical aptitude test. Answer all of the questions as fully as possible. Wait for your results on the site, so you can see how you would have performed if it had been the actual test.
Read Barron's book, "How to Prepare for Mechanical Aptitude and Spatial Relations Tests," which offers valuable insight into the type of questions to expect and gives you hints to increase your score.
Take the practice test that comes with your registration materials.