The rest of us must rely on our curiosity. I wrote an article some years ago on curiosity for innovators (which I'm happy to share on request). It ends with a list of ways to develop curiosity:
- Put yourself into new situations that challenge your worldview (and imagine they are true)
- Actively observe, rigorously recording the input to all your senses
- Come up with your own list of great questions
- Question the status quo
- Give yourself permission to look at things differently
- Build your skills at investigating
- Have a perspective
- Make time for curiosity
- Be persistent
- Keep notes on your observations, insights and conclusions
- Solve puzzles
- Get other perspectives
The best question of all is "why?" The second best is probably "why not?" One way to come up with great questions is to reject conventional explanations (which is safe in fiction, less so in real life). We often accept a word as an explanation. (Why do things fall? Gravity.) That's never a sufficient answer. Probing more deeply can help.
I always recommend brainstorming, often writing twenty answers to a question, as a way to get to something that is surprising or even unique. One thing I've found is this does not work for everyone. They have a very difficult time generating a lot of answers, and they often twist themselves into pretzels to get "reasonable" answers. They are not comfortable with crazy.
And sometimes even highly creative people just run out of energy or feel stale.
For either of these, a return to the original approach to brainstorming is in order. Bring together a group of people and have them throw out answers (with no judgment). Reminding them of the basic rules of brainstorming can be useful, giving them permission to provide wrong and crazy answers.
What if people aren't available? One technique I've used myself is to imagine people I know well (either in reality or through their work) answering the questions -- what I call brainstorming by proxy. At times, I've taken this so far, in the case of fiction writing, that I have composed beginnings and endings for stories in the voices of writers I've read until I can write in their voices. That's going a bit far, but just imagining the answers from others may open you up to a kind of craziness that can be engaging and inspiring.