The reason I began visiting sites such as this, and about a dozen others I've partcipated in over the past few years, is selfish. This is a study aid.
What I found by visiting these sites is that a lot of questions come up that I can't answer off the top of my head. Some I don't have a clue about. Participating and forcing myself to crack a book or do a little research is a way to motivate myself to study. From participation on regulations boards to student pilot sites, I find that having a purpose in seeking a particular answer or researching a question makes study interesting. Just cracking a book for the purpose of study alone, I fall asleep.
Try picking a topic, any topic, and researching it. It's a good starting point.
Another reason for going this route for study was instructing. I enjoy it, but seldom get the opportunity. Providing instruction or teaching is perishable, like any other skill. The simple process of practicing an explaination quickly erodes, as many of my posts will attest. Given the limited opportunity to work with students, I've selected several boards at different times to work strictly with students or mentor up and coming pilots. Other participants hopefully gain something in the doing, but my own involvement is admittedly for selfish reasons. It's me that benifits by participating; it's an exercise.
Flash cards work for aircraft systems and performance numbers. I take a lot of notes in books, highlight them, write in them...I even go so far as to color the pictures in diagrams when I get really bored. When that fails, I'll go to the shop or the hangar and study, or dive into the maintenance manual for specifics.
You'll find that the ways to study are nearly endless. When learning a new aircraft type, I find that getting in the cockpit and running the proceedures over and over helps. I tack cockpit posters to the wall, and put up all the memory proceedures and items around them on 3X5 or bigger cards, and review them ten or twenty times a day. My regulations are dog eared, highlighted to death, cross referenced and indexed, and beaten up (and each year, on or about new year day, I ceremoniously execute last years copy with a .45. It doesn't help me study, but it sure makes me feel better). Be creative.
Find what works for you.