Have a notebook
The sketchbook also allowed an artist to develop their own style and repertoire, an additional memory bank that collected a body of material to refer to at a later date.
And take a note... with slight strokes in a little book that you should always carry with you... preserved with great care; for the forms, and positions of objects are so infinite that the memory is incapable of retaining them, wherefore keep these sketches as your guides and masters.
"Hockney's telling point is that it is not enough merely to look at a work: if an artist wants to learn from it, they need to make their own record of it, and in doing so, come to fathom it better."