The size of the wood planks depends on the look you want to achieve. For a modern, sleek appearance, use narrow planks around 3-6 inches wide. Wider planks, typically 6-12 inches, give a more rustic or traditional feel. Long planks create a continuous, seamless look, while shorter planks can add texture and depth. Consider the size of the room as well; larger rooms can handle wider planks, while smaller rooms benefit from narrower, less overpowering pieces.