It's all about the relationship first. Many newbie business owners give a proposal to anyone that they think seems interested in their services. That is an easy way to waste your time. Before you submit a proposal, you should have already developed a strong relationship with the buyer and showed the value that you are going to deliver. Your proposal should be a reiteration of that value and relationship and should only be submitted when you know that you are going to make the sale.
When new freelancers are creating a business proposal template that they are going to use often, they usually miss the most important pieces that make the difference between a good proposal and a proposal that sells. By emulating the sales process, you can create a proposal that solidifies the relationship that you've built with a prospect, and reinforces the close of your sale.