Everyone here is giving you great advice, but what only lowengard told you is that a proposal is all about what you want. If it is a contract then you should have your company lawyer, or personal lawyer check over the contract depending on the amount of time or work you are going to have completed. If you are entering into a $15,000 contract + possible retainer work, then you will want to have a lawyer check it over. If you are entering in a $500 contract for a one time fee, then you would be quiet alright creating the proposal in a way so that both you and your client can understand it and get a portion up front.