Hi Elizabeth, my name is Cassie Smith and I've worked closely with several event sponsorship coordinators for a handful of big festivals.
Those I have worked with have expressed how so much of their job is simply sales. They often create a slide deck with an outline of the event, and statistics - how many attendees, audience profile (age, gender, income bracket, interests, etc), how many different attractions, social following of the organizations involved, etc. Also, having a quote or testimonial, or simple case study of the success of previous sponsors of previous events can be really effective. They do as much as they can to illustrate the value the sponsor will get out of participating rather than explaining the need you have for sponsorship dollars. William Chipps, Senior Editor of the IEG Sponsorship report says, "While corporate interest remains high, (sponsorship) spending growth is hampered by (event) organizations that continue to sell need-based sponsorships, not marketing-driven solutions (to potential sponsors)."
If you don't have all that information on hand, don't stress. Just work with what you have to create the best picture of sponsorship opportunities.
Additionally, IEG did a big survey of sponsorship brands, and found that the top 2 things brands look for out of sponsorships are 1) general awareness of the brand and 2) general awareness of the sponsorship itself. If you can show how you'll brag for them about the fact that they sponsored your event, that they are giving back to the community, that they are a socially responsible brand, you'll meet that need of theirs.
What kinds of brands are you looking to gain as sponsors? What are some details about your event? Happy to talk further.