First section-In this section write about your pleasure to be associated with this esteemed company XYZ. Write about the main point of your proposal and what you aim to achieve by it. You must mention the qualities that you possess and why you wish to be associated with this company. You must modestly and briefly mention your success rate in other similar endeavours.
Second paragraph-This section is very important since you have to be clear about your major goal in this section. For instance, in case of a proposal with a school you must mention how the students shall benefit from your endeavour and why they should back you up in this.
Last section- In here briefly add on a parting note your interest in working with the firm/ organisation. You must remember to enclose the formal proposal and ask the authorities to contact you in case they are interested.