Four steps - one way to start a painting
This is how I usually start my paintings. I set up the still life in my shadow box with the light coming from the left or right, just so there is a strong shadow side with a cast shadow.
One way to start a painting:
Step 1 - after toning the canvas with a wash of ultramarine blue, cad red light, and yellow in a neutral mix, the next step is to start drawing with the neutral mix. Keep the drawing to shapes and values more than a line drawing.
Bottom left is a value drawing of shadow, cast shadow, reflected light, and light. It's all about getting the values right.
Step 2 - Top left - Translate the values to the equal color values, still very loose and thin paint. At this point, still looking at the sill life is a good time to do any needed re-drawing.
Step 3 - Top right - apply thicker paint, add mid value where the dark meets light and on the right side of the apple that reflects the light. I start with the darks first.
Step 4 - Bottom right - Finish the painting by refining details, adding thicker paint on the light side, adding the highlight, The general idea is to work all over the painting including the background and foreground.
There are lots of ways to start paintings. This is just one.