T-Shirt designs - Need help!

Well I tried to make my own T-shirt once and it turns out I don't have the right printer to make one. So it came out kinda bad...

Anyway, one day I hope to actually get the right kind of printer and make my own T-shirt. The thing is...looking at my messed up one it's not really starting to look like something I would want. Well actually I would want it but doesn't really fit my needs.

I'm a huge Elfen Lied fan and I plan on making a T-shirt design with Lucy in it. I'm just not sure how I want to make my image. If someone has any good ideas or suggestions on making a T-shirt image then please help. The maximum image I can make is the size of a piece of paper (8x11 or something). It can be smaller and I can cut off any access crap.