These are interesting questions, Julia.
In a nutshell, I ask the potential client a few questions that tell me a lot about what they want.
The first one is, “Who’s your audience?”
The next one is, “What do you want your readers to do as a result of reading this?”
There are topics I prefer and ones that I’ll stay away from. In most cases, I learn more about what’s required before I make a decision.
What your questions have done, however, is remind me that I need to prepare a bit better for when the opportunities do arise.