Michael Prescott has a nice write-up of tips for Patreon (and similar) campaigns:
1. Explain what your project is immediately—ideally, the very first sentence. Every paragraph between the start of your Patreon pitch and that will cost you 75% of your remaining readers.
2. Describe the value that your Patrons are getting. So many pitches explain how the money will be useful to the creator, or try to bank on our fondness for the creator as a person.
Read the rest of his 10 tips (numbered 1 – 9) in his “Tips for Patreon Campaigns“.