It’s a little bit of an art vs a science. When I was working in public media we would try all sorts of messaging to find what resonated the most with our audience, and get them to become “members” (donating on recurring basis). This involved segmenting the audience and doing some basic multivariate testing where we would change the copy, graphics, and CTAs. It was trial and error for a bit until you recognize patterns.
Here are some examples from HubSpot: