When you meditated on self-acceptance, for example, you desire to create a reality where you love and accept yourself. In this process, you gain self acceptance.
When you meditate on a better memory, you are creating a reality where your memory is better and it serves you well. As you meditate on your memory and visualize your memory serving you well, your mind creates a better memory.
If you are meditating on improving your memory so you can recall your astral travels, your mind will visualize this happening. Your mind will then start to accept what is seen and experienced on the astral plane and you will start to recall your astral travels.