I usually take a white pencil, turn the t-shirt inside out and draw where I want cut out.
For instance, for the kind of shirt you might want, I would make a deep scoop neck in the back. Or you can just make one big cut down the middle of the back and tie it in random places.
There are ton's of sites online that can give you ideas, there is also a book:
http://www.amazon.com/Generation-T-W...1458541&sr=8-2
which is probably the most awesome diy fashion book there is
here is LJ's t-shirt surgery:
http://community. l i v e j o u r n ...tshirt_surgery