My friend Jonas Salzgeber recently commented on the phenomenon where we take the time to learn things that will improve our lives, yet fail to properly apply them. In my experience, a major obstacle to putting what we have learned into practice is information overload and it's accompanying disorganization (not just the force of old habit or the lack of will to change - although these are major obstacles too!) Without proper organization and memorization, what sticks in our head after reading a good book or watching an interesting video is piecemeal. It's a matter of chance whether we remember and apply it, despite our best intentions.
The ancient schools of philosophy had their own solution to this problem - handbooks. These were collections of useful and powerful phrases that the students memorized and kept close "at hand," for when they were most needed - in instances of challenge, stress, or trouble. As we'll see, the handbook is the most powerful tool in our arsenal for growth - both an organizational aid for our hectic lives, and a method for directly improving our habits and thinking.
The Role of The Handbook in Ancient Philosophy
Ancient philosophy was designed to be memorized, so that it could be “at hand” when we are confronted with tumultuous situations…The teachings of Stoics, Epicureans, Cynics, Pythagoreans, and Platonists were often condensed into short, pithy maxims designed to be easily remembered so that they would pop up in our heads when were are in stressful situations...The students wrote these maxims down in their handbook, memorized them, repeated them to themselves, and carried them around–that’s the point of a handbook, so the teachings are procheiron, or “close at hand.” 
This practice was used particularly by the Pythagoreans. Memorization and maxim had an important role in the Pythagorean way of life - they understood how irrational people can be. Philosophical theory alone is not enough to transform us, although it certainly has its place.
Information Overload - How to Organize Important Ideas
Keeping ideas organized requires some tips and tricks and I'll share what has worked for me, now that I finally feel like I have a decent system in place. Even though I work in a field based on organized access to information, I know a thing or two about disorganization too! I had for years dog-eared and annotated my books while I read, but not always gone back to do anything with the notes.
Ebooks and Kindle format books have some advantages, including the ability to easily highlight and search for a specific phrase or passage. But I usually only buy a book in digital format if I expect to read it once. I buy paper if I like a book enough to have in my collection and read over and over again. There is just something great about a paper book, the feel of it between your fingers, the smell of the ink, the ability to annotate it, and so on.
For books that contain information important enough to refer back to, I suggest keeping a reading notebook with the page number and any memorable quotes or descriptions. It's quicker to do this while you are already reading a book on a particular page than to waste time flipping through trying to find it again later. It's especially important to do this with books that you borrow from the library or that you won't always have access to.
Organizing things online is easy because there are so many apps and tools available, and because certain platforms (like Youtube) allow for internal bookmarking. Pinterest is my go-to bookmarking tool for images, blog posts and web content. In addition to all of the boards I maintain for the blog, I also have many private Pinterest boards that I use to organize recipes, parenting tips, and so forth. I also like Instapaper for bookmarking websites.
Creating A Handbook
A handbook is different from a more general organizational tools like a reading notebook or bookmarking apps as described above. The handbook is reserved for only the most essential phrases and ideas that you absolutely don't want to forget. My handbook is a small notebook that I carry in my purse and always have with me. Whenever I come across something extraordinary that I want to memorize, I write it down and refer back to it, so that applying it eventually becomes second nature.
Jules Evans used an ancient philosophy-inspired handbook to improve his mental health and revolutionize his life:
"I also carried around a little handbook like the ancients used to do, in which I'd written some of the "power phrases," from the therapy course. When I felt really stressed, I would retreat to a private space, pull out the handbook, and repeat a power phrase...It was not enough just to have a one-off ephiphany into how my thinking habits were causing me suffering. I had to take a systematic approach to creating new thinking habits - and the art of memorizing and repeating maxims was crucial to that process." 
The best thing about the handbook is that you can target it to your unique situation, recording what is most helpful based on your strengths and weaknesses, and omitting the rest. You might especially want to write down phrases for when you are stressed or troubled. The Stoic philosopher Epictetus felt that this type of practice is the quintessence of philosophy, helping us to overcome challenges and live the best lives that we possibly can:
"Philosophy's main task is to respond to the soul's cry; to make sense of and thereby free ourselves from the hold of our griefs and fears...True philosophy doesn't involve exotic rituals, mysterious litergy, or quaint beliefs. Nor is it just abstract theorizing and analysis. It is, of course, the love of wisdom." 
1. Evans, Jules. (2013). Philosophy for Life and Other Dangerous Situations. 116.
2. Ibid., 124
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