Some other methods that can help you retain more of what you learn each day involve what you do at the end of each practice session.
Let's say in one session, you work on a section, however many bars it is. When you're done, before you leave the piano or go on to the next thing, you should take a minute to look at what you've just worked on (imagine you're imprinting it in your head.) Let the passage run through your head. Esp if it's at a higher tempo, and esp if you've been working on getting it up to speed, play through it one last time, very slowly. If you're doing something HT, play through it HS before putting it away. These sorts of things help you to "imprint" that section on your brain and make it more likely that it will sink in over night and while you're away from the piano.
Now, let's say you're going to work on another session. Before you do that, get up, walk around the room or go into another room and come back. It doesn't matter really, but just give yourself a little break. I have found that doing this takes away some of the frenzy I might accidently create while practicing. I love to play more than anything in the world, and if I don't catch myself I could just sit at the piano forever, never getting up or a taking a rest. But I think this is not only bad for the body (back, shoulders, wrists etc) it also is stressful on the brain. Give your brain a chance to process what it just did, before you move on to the next thing. Also of course, remember that you need to "sleep on it."
Now it's the next day. You take out the score and are ready to start. Don't just jump right in. Look at what you did yesterday. I have gotten into the habit of having a piece of paper along with each score that I write notes on about what I practiced, what I should do the next day etc, so I look over that and it really is a memory-jogger. Think about what you're going to do, look through the section through to the end of it (if it's two notes, it's two notes, if it's 6 bars, look through 6 bars) And then, after you've done this (it hardly takes a minute), start to play.
These things should all help you retain more from the previous day's practice. But here comes the final thing that I learned from both Chang and Bernhard. If you start to play and it feels like you have literally lost all of the progress you made yesterday, don't fret about it. If you think "oh, I forgot everything! this is not working! I am a terrible pianist!" all you're doing is putting a negative mode onto yourself which will just be a detriment, you'll feel pressured and defeated before you even start.
The better way to react if you find you've forgotten everything is to say to yourself: "well, that's how it works. I remember something, forget it and then remember it again. this is like a three-step process of how the brain learns. nothing wrong, I'm just at step two right now." If you think of it this way, forgetting then seems like a necessary phase, rather than a cause for frustration, you can actually congratulate yourself: "I learned something, and now I've forgotten it. I'm doing exactly what I'm supposed to be doing." If you approach it with this attitude, re-remembering it (re-learning it) will a snap.
My two yen, for what they're worth (108 to the $ I believe)