The best way to remember something is to make it memorable!
To that end, it is not enough to merely think of something. You also need to think about it. And two powerful ways to accomplish thinking about something are Association and Elaboration.
Association
Your ability to remember things is greatly enhanced if you can associate them with things you already know. This process is called anchoring. When you relate new information to solid, pre-existing knowledge, it becomes securely anchored, just a like ship to a dock, ensuring that the new information will not just drift away with the passing tides and currents. Such anchoring breeds security and confidence because it takes advantage of pre-existing memory channels that we have previously worked so hard to create. By the way, these associations should be natural and meaningful, not contrived… not based on clever mnemonic tricks. Of course, the more anchors, the better!
As you study theory and scales and chords and ear training, you will discover that music is not a disconnected collection of isolated parts, but a tapestry that is richly interwoven. For example, scales and chords are just different views of the same musical stuff. Also, learning new scales and chords is easy if you relate them to scales and chords you already know. The lesson here is this: Always relate new things to things you already know!
Elaboration
When we are tired, stressed, distracted, or under pressure, it is easy for our brains to “forget” things if we only know them in one way. When we elaborate on something, we explain it in more than one way or add or emphasize important details about that something. Elaboration builds confidence and security because it creates a rich network of connections that employ more than one part of our brain. Of course, the more elaborations, the better!
A common musical application of elaboration is to see a melody as more than just abstract letter names. We can also see the melody as Solfege syllables, a rhythmic sequence, a harmonic cell, a visio-spatial pattern, a fingering pattern, and a physical choreography.
Analogies and metaphors are great examples of elaboration is action: How is this thing I am trying to learn like something else I already know?
The takeaway: Always try to learn things in more ways than one. Your confidence will grow immensely with every new pattern and connection you discover!