A still life is a composition of live objects! While the direction of the lines or paint brush strokes makes handling volumes easier, your perfect mastery of color is what gives them realistic contours.
In order to visualize the play of light clearly, make your source of light as bright as possible while you're making your preliminary sketches and getting the three types of shading facing you onto paper:
Every drawing material captures light differently: shining on glass, more subtle reflections on metal, and hardly perceptible on wood…
Colors influence each other: a crimson tablecloth inevitably introduces a little warmth into the colors of the objects placed on top.