I am also in the process of writing a proposal... have you checked what is expected of the department you are applying to? I think requirements really depend on the Uni/department and what area/subject you are looking into.
From my experience, I have had to write a brief summary of the area/research topic, research questions, relevant literature already looked at (properly referenced), methodology and any previous experience had with the subject or area of research. This was what i have picked up from the specific institution details though, so it's worth checking with yours ;)