I know that I want it to be:
all or mostly black ink (wouldn't rule out a highlight or two of color, but I don't want it to fade)
be in a relatively non-painful place (staying off shoulder blades, spine)
be in a relatively non-stretchable place, keeping in mind that I want to have kids (staying off the stomach, breasts, and hips most likely)
Strongest candidate for a location is my right shoulder/upper arm, just due to process of elimination and the fact that I want to be able to see it without looking in a mirror.
As far as what I want it to be, most of my ideas have involved something feline; first I was thinking a cat sillhouette, then leopard spots. I've also been thinking something with magickal elements, like a glyph made from the Greek letters for Thelema or a unicursal hexagram or something along those lines. Problem is I'm relatively paranoid about this being something that will be a part of me for the rest of my life, and want to make sure that it is something I will want for that long. I've always been a cat, so that's a reasonably safe bet. While I feel very strongly about Thelema/magick, that's still a relatively recent development, so who knows for the future. What I really need is something that represents a fundamental part of what I am, and faced with that challenge I keep drawing a blank! I also really like tribal/celtic designs, so maybe I'll just end up with something like that.... I very much want to design it myself, too, or at least come up with the basic idea myself.