Remember, there are a couple of high level objectives you want in any
proposal. This goes for when you finish your PhD and go onwards to do
grant proposals too.
That you know the field that you are proposing to do research in.
(assessed through related work, references to current and past works)
That you are an authority in this field (optional)
(assessed through your individual work in this area)
That the work you propose is feasible
(shown through your preliminary results in this area, (optional)
external referee reviews,
and a realistic timeline and milestones for completion)
That you are the one who is best poised to do the work proposed
(this should be self evident through a combination of 1+2)
That the proposal is a finished product
(proofread, complete, good figures and good organization -- the
latter meaning that less important information is relegated to
appendices)