Once the layout is projected onto the drawing board, the sketch must be refined. The more precise and detailed the lines are in the drawing, the better the painting will turn out. I use several drafting tools to obtain smooth arcs, straight lines, ovals, etc., to create the car's diverse body-lines. My favorite tool is the blue flexible pen guide that allows you to shape it to any curved or straight line. Use a light touch with a #2 pencil as you refine, then use a heavier line for the final lines. The kneaded eraser is great for erasing lines without smudging or tearing holes in the paper.