You now have your practice log, and now it's time to get organized. The practice log does more than just remind you of what pieces you've practiced and what you need it do. It also helps you keep track of landmarks.
Landmarks are, in short, rehearsal letters. (Orchestral players know what these are, but keyboardists may not. These are editorial letters in scores so that the conductor can tell everyone to start at "C" or "D" or wherever. This works beautifully, except when the conductor has a different edition from the rest of the orchestra.)
As you know, solo repertoire doesn't come with rehearsal letters, so you're going to have to make your own. But before getting into how to do that, we should consider why we're doing this at all.
Landmarks are those places to where you'll jump backward or forward when you have a memory lapse. (I write "when" because it's going to happen sooner or later.) Landmarks need to be in logical places, and they also have to be in places where you'll be able to make a seamless transition. In other words, landmarks should be where phrases naturally rest. Yes, it's really important to know the music theory behind your score, but you don't necessarily need to know the theory to find the phrases. Use your ear and your instinct.
Placing landmarks is kind of fun, because it's nice to see a piece break up into manageable sections. Sometimes, in a piece with which I'm very familiar, I'm able to mark landmarks right away. But if I don't know a piece too well, I'll add landmarks much more carefully, only marking them out as I work my way through the memorization of the piece.
Sometimes I use actual letters, but the problem with letters is this: They're much too firm. For instance, I'm currently working on the third movement of Bach's Concerto in d minor. I finally got around to working on my letter "N," only to find that my "N" was much too long. Since I'd already written "O," the temptation was to just deal with the long "N," and tolerate the fact that this landmark was too big. But that's not good practice! (Remember patience...) So, I ended up creating N1 and N2, a simple solution. More often than not, however, I tend to draw asterisks in my scores. I don't feel a need to enumerate my landmarks; I only need to know that they're there.
Some writers on memorization have said that you should be able to begin playing from anywhere in a piece. They also suggest jumping around in your practice, apparently so that you'll be able to recover from anywhere in the score. But this only confuses matters. Knowing that audiences expect musical phrases, we can assume that musically placed landmarks will help you survive lapses in the most musical manner. Jumping from, say, measure 101 to measure 55 just because you can is not a musical decision. Be logical, be musical.
Once those landmarks are placed--and remember, they can always be changed or moved--, I begin work on the piece. Lately, I've been doing the following: I memorize the final landmark and then go to the first, then the penultimate, then the second. This seems to pace things patiently, and it keeps me from becoming too excited about finishing a piece. Believe me, I've memorized pieces where the last page isn't memorized as well as the rest of the piece. That's happened when I've rushed the process out of impatient excitement. (Well, it is fun to finish a lengthy project!)
In the case of the Bach concerto movement, I've been leapfrogging landmarks (A-C-E-G, etc.). I've gotten to the end of the piece, and now I'm filling in the blanks (ABC, CDE, EFG, and so on). In my just-started C# minor Fugue (Bach: WTC I), I decided to begin on the landmark at the top of each page and work my way down, thus trying to learn four landmarks at a time. While I make many of these choices for the sake of variety in my practice, in the case of the Bach fugue, it's a piece I have never played before nor heard much at all. I don't know where I'll ultimately be putting my landmarks, but, by jumping around, I'm able to keep better musical track of the scope of this five-voice fugue and Bach's magnificent voice-leading.
This brings us to the most important part of landmark work. Once a piece is memorized, one must know the landmarks backwards and forwards. Indeed, knowing the landmarks becomes, in some ways, more important than knowing individual notes. I make sure that I'm able to start from each landmark; that I know where each landmark sits in the score; and that I'm able to visualize each landmark's starting point. When I have a piece memorized and I'm working away from the instrument, I don't visualize the piece from beginning to end. Instead, I work from the last landmark to the first, making sure that I am fully able to be at any section of the piece at any time as needed.
A final work with regard to concertos: In a concerto, you have nowhere to go but forward. The orchestra is dragging you along, but only in the forward direction. But in a solo piece, you can easily get caught in a loop, start over again, or who knows what. In this regard, I tend to think of concertos as being two-dimensional. They can only go in a temporal line from here to there. Solo repertoire is three-dimensional. In a lapse, solo repertoire has the potential to go up, down, left, right, backwards, forwards. Thank God for landmarks!