From Harry is Immortal to Dumbledore is actually time-traveling Ron, Fan Theories have long played a central role in uncovering the secrets of the series. And just when you think you’ve heard them all, someone comes along with something that makes you crack open the books and start looking for clues all over again. Never hurts to brush up on your Gamp's Law of Elemental Transfiguration, some Arithmancy, and of course the New Theory of Numerology (even Hogwarts makes you get the newest version of the textbook apparently)
Also take a look at the Magical Games and Sports going on as well as some Illuminating Polls to take.