In terms of messaging, I take a lot of inspiration from subreddits by going into discussions, seeing people's pain points (as they relate to the products I write content for and what they're trying to solve), get a vibe of the language people are using, and then create a swipe file. From there, as I'm planning my landing page copy, at times I'll comment on threads and find ways to naturally inject the messaging I'm planning to use, and see if it resonates. But that's a very roundabout way, kind of convoluted way of doing things.
Another tactic I've used working for B2Bs is it to get the salespeople to ask how someone who requested a demo discovered our product—a lot of times it's through blog posts and landing pages—and to flat out ask "what was it that resonated with you?" A lot of times, people have been pretty forthcoming about what aspects of our messaging most resonated. Again, that's a pretty drawn-out process though.
All in all, there aren't really any shortcuts. Using something like SEMrush's SEO writing assistant helps for making sure you're writing succinctly and hitting certain keywords, but other than that, a lot of times you just need to publish a page and promote it on social media to see what sticks, and then reference metrics like clickthrough rates, etc., to see how well your messaging is performing.
Forget the Funnel has some great resources on this topic: https://forgetthefunnel.com/
I hope that provided some insights. Go Ducks!