The processes of memory include encoding, storing and retrieving. Without going into too much details what these processes are, to improve memory, we must work on enhancing all stages of memory.
To improve encoding, we need to work on making information easier to process. In this case, generally how we visualize or hear the information. You could enhance the ways you see the information by making your notes easier to read with shorter sentences and more explicit details. Try to avoid making your notes ambiguous or unclear. Clearer points are easier to remember. Furthermore, attaching pictures or symbols to your notes can help you brain tell apart different concepts. Highlighting or bulleting your points so that the notes follow some structure or pattern help memory too. Your brain really likes patterns a lot and things standing out.