First, be realistic and allow yourself the time to focus on preparing and studying. As someone once told me, "you need only to take the test once to pass", so dedicate time to this endeavor and to passing. Do not take-on extra activities and discipline yourself to stay with-it and reach your study goals. When it's all said and done and you have earned your PHR designation, it will all be worth it!
Join a study group, or find one online through HRCI and SHRM. Many local SHRM chapters offer in-person groups (usually for a cost), which are especially helpful. Marathon-sessions work well for some, but most people find they can absorb the materials better over time, so groups which meet once a week for 12 weeks or more are useful.
Use a variety of study materials, even if you go to a class...from the Mathis-Jackson book to the SHRM Learning System, none are endorsed by HRCI. It's best to take a well-rounded approach and use many different qualified sources for preparing.
Learn how to take a STANDARDIZED test! If it's been a while since you have taken a four-hour long exam, 225 questions - then you need to practice. There are many free tests online and some you can purchase for a fee, but a class or study group will also provide practice tests. Find someone you know who has taken a standardized test recently, and ask them to coach you (only if they passed! haha). Be strategic about what you are facing and remember that all these tests are essentially the same - you CAN do it!
Learn your terms, laws, and establish your body of knowledge - then learn how to apply the right information to the right situation. Use flash cards, make audio cd's, review notes, read...know your learning style and use that to your advantage. Practice your test-taking skills and don't give up! Talk to people you know who have been through the test and find out what helped them pass and be successful.