Creation As Texture
The act of creation is a simple matter, and in any medium it is the same. An object is texture, and creation is a matter of conformation of a random mass to the desired texture.
Each element of a painting has a texture, clouds, rock, folds, flesh etc. and by exposure to those things a bank of imagery is built up in the mind of sufficient comprehension that those textures can be chosen at will and built from a random form. The clouds I paint begin as random shapes, as do the rocks, and these are guided into the final states using only the image bank.
Music is built in the same way. Different passages of music evoke different moods and textures in the same way as different object in a painting, and a tune of random notes can be modified and pushed towards the desired texture. As in visual art a resource bank of melody and chord combinations is necessary.
The same is true in literature, or any other art form. It's a matter of deciding on the texture desired for each section, and building up a sufficient image bank of the sort of texture to fit.
Conclusions
A good memory really helps creativity because this acts as a resource bank of texture. This explains why a good writer is a good reader, but it also limits the output of the writer to the types of things he or she has read.
A short term revision of the sorts of texture needed for a particular passage (whether in music, writing or painting) is useful, and a bank of textures is essential for a great artist. Just as a reference guide to different forms of trees would be needed for an artist who paints trees, a writer will need to read books of different styles, that correspond to the types of moods they require during writing.
Painters who rarely look at new images will end up painting similar things in cycle. Musicians will end up writing similar music, and writers will end up writing similar books. To be truly diverse as an artist it is essential to have wide eclectic tastes, or even if not enjoyed, wide exposure to different types of image, music, book and other art forms. Limitations of taste must be overcome and diversity embraced.