There are different types of proposals, including: for university theses or dissertations, for non-profit grants, for research grants, for businesses and for projects.
To write a thesis or dissertation proposal, see http://pwr.la.psu.edu/resources/graduate-writing-center/handouts-1/WritingProposals.pdf/
To write a grant proposal, see http://www.sacredheart.edu/officesservices/foundationsandgrants/proposalwritingformats/
To write a research proposal, see http://libguides.usc.edu/writingguide/researchproposal
To write a business proposal, see http://business.lovetoknow.com/business-proposal-format
To write a project proposal, see: http://www.writing.engr.psu.edu/workbooks/proposal_guidelines.pdf