Freelance devs building things with non-technical ‘idea’ people: how do you wish they’d present their ideas?

Non-technical person myself who dabbles in app ideas. I could use advice on how to optimize this process:

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• what documentation do you want me to hand you?
• to what degree should I dictate every step of the way without being overbearing?
• what are the common pitfalls and how should I avoid them? (etc…)

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Obviously I'm looking for the most efficient path to completion, as I imagine you are too. Who's your dream client and why?