One of the main problems in the Schiavo case is the absence of a living will.
Terry Schiavo never put it in writing whether she would ever want to be kept alive this way. A living will is basically a declaration of what you want to happen if you are ever on some sort of life support and unable to tell doctors your final wishes.
In Schiavo's case, a living will would have saved a lot of legal arguments between family members.
Jason Armstrong, an Attorney at Fenley & Bate, L.L.P. said, "mom and dad say one thing, husband says another. At least if there was something that she had signed and formalized, it would give him something to go to the courthouse and say 'this is what my wife wanted.'"
A living will can also be used to specify what you want done as far as medical procedures. If you have certain religious principals as far as medicine, a living will can prevent any unwanted procedures.