When changes are desired, I begin by drawing or creating models. There are several techniques for creating these: watercolor, acrylic or oil paints, gouache, and others. Personally, I like to draw pictures using a fountain pen. At times, I will use colored pencils on a colored canvas. I adore the quality of a fountain pen when shading, as it conveys the depth of the composition in the picture, highlighting small details to take note of. https://www.elinarti.com/en/portfolio/pictures-modelling/