Remind them why they need you. Your proposal should immediately remind the prospect of what their problem is and why they are talking to you in the first place. In other words, you should immediately start your proposal off with the pain your prospect is feeling. Are they not making enough sales? Is their message not getting out to their audience? Could their life_savings be in jeopardy? They are talking to you for a reason.
Then, deliver your polished proposal. Save it in a PDF file or print it out, or both. The best delivery method for you depends on your relationship with the party who will receive your proposal. It's common to attach PDF files to email these days, but for your situation, it might be most impressive to hand_deliver a nicely printed and signed proposal.