You can look online for sample proposals that you can work from, in many cases you will be able to download a template that you can work from. You will most likely find that there are dozens of sites offering hundreds of different templates to download. It may take a while, but you will find that there proposal forms that will match almost any need including yours. Take your time and select the one that best suits your needs.
If you work in a Human Resources/Personnel department at a large corporation, or work for a small agency that sells temporary labor or executive search services, then you're in the business of evaluating personnel needs and pitching people and their skills. You may need to convince your boss or a new client of the need to create one or more new job positions, or persuade the boss or client to fill existing positions with personnel you recommend. Perhaps you are persuasive enough to do that with a phone call or casual conversation in the hallway, but odds are better that you will need to write a proposal to pitch your ideas and persuade the client or upper management.