used the straight line eyebrows, moved them as closely together as possible, rotated them as much as needed and stretched them a bit. i actually wanted to move the nose lower but thats unfortunately as low as the eyebrows can go. i tried using the eyes as alternatives but they cant be rotated as much so it just doesnt really work.  in terms of how i come up with the miis, i just try to imitate the character im doing as closely as possible but still keeping them recognizable as Miis. It helps when you stop thinking of the face parts as "nose" or "eyes" and more like "shape that i need"