I am doing an exercise using simple washes and lifting-off techniques.
I have done the drawing. This is for the highlight, as the light source comes from the right, the shadow side will be on the left of the apple. I use a flat brush to wet the apple area before I apply the first wash. I first paint the yellow color in the light area, then I quickly clean my brush and put the red color to cover the apple. Because I have my paper tilted in a slight angle. The red paint is now coming down, even wash over the yellow. I clean my brush and squeeze off most water, then start to lift-off the paint around the highlight area. Sometimes I need to do it a couple of times before I can get the result that I like. This technique can give us a nice, soft natural glowing highlight. Then I mix a gray color for the cast shadow.
Before I go on to the next step, I will wait for a few minutes for the paper to dry.
This time I start from the shadow side of the apple. I mix blue with red for a dark red purple color, and paint in the dark shadow area. Always keep referring to the photo or the live setting that you are painting from, to observe and analyze before each action. Now I add more red to my brush and paint in the transition area between the light and shadow. Sometimes I use the full size of the brush and sometimes I only use a portion of it to paint. Now I like to use a dry brush technique to create the apple's skin texture. I clean and dry my brush, and I move my brush upward from the existing wet paint. This works well for creating this texture look.
Next, I am going to use the lifting-off from dry paint to create the reflected area on the left. I clean my brush and squeeze off most excess water. Then I start to loosen up the paint in this area. I clean my brush again and dry it, then start lifting-off.
After the paper has dried, you can use the overlaid wash technique for further development if you need to.