Idea communication

Hey everybody! So I was hoping someone out there could point me in the right direction, here’s the situation: I’m shopping around for a software developer to consult with a project. I have the idea / set of functions I want the software to do but I’m not a developer and even though I know in my head what I want it to be I don’t want to waste their time or my money going in there saying stuff that isn’t helpful to them because it’s too vague. So the question is: is there a set of questions out there (or diagrams to draw) that I can answer ahead of time so the meeting is as productive as possible?