Your Dictionary's website provides a good example of a written proposal. The example breaks the proposal into sections, including the contact information header, purpose statement, problem and evidence, proposed solution and the cost of said solution. The proposal ends with a conclusion section that summarizes the problem and solution while highlighting the impact that the proposal's approval would have on the affected population.
The purpose of any proposal is to convince someone that the stated method of action is the best way to solve a pre-existing problem. When writing a proposal, keep in mind that the readers need to be swayed by the writing, as they have their own needs in the forefront of their mind. Additionally, the readers are likely to spend minimal time addressing the proposal, so it needs to be brief, specific and impactful.
The general rule when writing proposals is to start by stating the information that will be discussed, state the information, and conclude by reviewing the information stated. This clearly delivers the message to the readers, and the repetition of the information keeps the proposal's topic in the front of their mind. Play to the readers, highlighting the benefits that can be provided to them if the proposal is approved. Stick to the strategy of keeping the proposal brief, specific and impactful by utilizing bulleted lists, pictures, graphs and charts. Write in an active voice, and make sure to clearly spell out all information to make the goal of the proposal obvious.