One of KM Weiland's pieces of advice in Outlining Your Novel (though this is actually in chapter "Before You Begin Your Outline") is:

"If you could have a professional reviewer read your idealized concept of your finished book and totally get it—completely understand everything you're trying to say with your characters, plot, dialogue, and themes—what would he write about your story?"

And then you, being specific, thorough, and extravagant, are that reviewer.

OKAY THAT SOUNDS LIKE FUN wait how do I do that