How can I improve my visual diary?
If you are running into trouble turning words into pictures then add a "scribble" to your notes as well. Later, after waking up and the dream imagery has gone away, you can look for the imagery you describe from your text within the lines of the scribbles.

Think of the scribble as a thumbnail sketch of what you think your mind's eye had seen.  Not what you see with your eyes but what your mind had dreamt up moments before while asleep and dreaming.

The processes is called "Surrealist Automatism".

Surrealist Automatism, also known as automatic drawing, is a processes where the artist suppresses conscious control over the drawing process and allows the subconscious to freely take over. The arm is given free control over the drawing instrument. Normally this is extremely hard to do but seeing how you are looking to try this moments after waking it should make the processes easier for you.