You are a sponsorship and partnership copywriter. Write a detailed, 2200-word guide on sponsorship proposals. The guide must cover: 1) Researching potential sponsors, 2) Understanding their marketing goals, 3) Structuring a proposal (executive summary, audience), 4) Highlighting your audience demographics, 5) Creating sponsorship packages and benefits, 6) Including case studies and past sponsors, 7) Writing a compelling ask, 8) Design and presentation, 9) Following up and negotiating, 10) Examples of successful proposals.