Read it, write it, learn it.
I'm currently embroiled in studying Winning Chess Combinations by GM Yasser Seirawan. This is the first of his books that I have read, though I have been familiar with the high reputation of his work for years. Many improving players have had great results by studying his chess series.
I've also read bits of another book on chess improvement, Chess Master at any Age, by strong amateur player Rolf Wetzell.
What do these two books have in common?
The authors of both books advocate keeping handwritten notes on what one is learning. GM Seirawan, amazingly, has filled 32 notebooks during his chess journey. In his book, he repeatedly urges the reader to create a loose-leaf notebook organized into sections, each section representing the many different chess tactics, principles, and concepts one comes across during one's studies. For instance, one would create sections titled: Backrank Mate, Pin, f7/f2 Sacrifice, Perpetual Check, IQP, etc. In each section, paste in several positions that illustrate that concept--preferably from one's own games or, alternatively, positions that are very memorable or meaningful to the reader. The idea is to only have a few examples of each concept and to update the examples as one runs across better ones.
Wetzell advocates something very similar and in much more detail. It is a key concept in his chess improvement methodology. Since I haven't read the complete book I'll refrain from going into the details but I highly recommend picking up the book to see his method of creating notecards of positions and how he uses them.
Both authors emphasize the point that these should be old-school paper and pencil notes--not an electronic database of positions. The point is that as one is learning, the physical act of writing about the position will reinforce it in one's long-term memory. I don't know the science behind this, but since my college days, this style of learning has been important to my own success. I am drinking the Kool-Aid.
I've been keeping my own chess journal since 2010. Some of the things I include in it are the analysis of games, notes from books I am studying, important positions that illustrate concepts such as the Lucena position, my opening repertoire, etc. The problem with the chess journal is that it is not loose-leaf. As I flip through it, there is no cohesion to the topics. It is literally a journal of my chess progress.
If you are considering keeping a chess journal or notecards, one difficulty is illustrating positions by hand. Here is one of my more pathetic early attempts at hand illustrating a position:
Recently I've found some 2"x2" Avery 22806 labels that work perfectly for pre-printing chess diagrams. And the diagrams have sticky backs so I can just peel and stick them onto either notecards or into my journal. I paid $15 for 300 labels at the local office supply store.
Now my diagrams look much better and are quick to put together:
The chess notation you see above is from Chess Master at any Age. It makes hand illustrating positions a piece of cake, even for the artistically-challenged like me.
In the coming weeks, I am planning to supplement my chess journal with a loose-leaf notebook as advocated by both authors. I've found a nice 5 1/2" by 4 1/4" loose-leaf notebook at Staples that should work well. When I get it set up, I'll be sure to post a few pics. I'll continue using the chess journal as I am now, for notetaking while studying books, for interesting positions and concepts I want to be sure to remember, etc. and I'll use the loose-leaf notebook for organizing positions into meaningful sections.