Next, drag the Bezier handles to improve the line's shape. The back one should be vertical and the front one should be at an angle of about -45 degrees.
Under the Rendering rollout check both Enable in Renderer and Enable in Viewport and then give the line some thickness. I won't give exact measurements, but try to keep the proportions in the image above.
Under the Interpolation rollout check Adaptive. Now the line is really smooth.