Ok, first off. Don't add to it. It will just look messy otherwise.

As for placement, well it depends on you. If you want people to see it, i suggest perhaps your wrist or ankle. (Obviously, the size will have to be smaller if you do choose a spot like that).

Personally, i think that the back of the neck would look good. My friend has some sort of Korean script that runs down the length of her spine and it looks crazy cool!

Oh and keep it black.