It boils down to having your core story first. Because the balance is struck when you have a commanding knowledge of all that is germane to the Story.
Also on the point of letting go of ideas, rest well in the knowledge that you can and will have more and better ideas!
Don't trust the first thing that pops into your head* 'cause so-called inspiration is often just recalling something we saw before and liked. True inspiration comes from delving deep into yourself and reflecting on what will truly tell the story best.
You have to know your basic setting.
Setting is:
* Period (era),
* Duration (how long through time is the story),
* Location (where does it take place) and
* Level of conflict (Internal, Interpersonal, Extrapersonal) of the story
Also Characters Are the Plot. And vice-versa.
Your story is about these specific events about these specific characters. If one changes, it affects the others, it has to otherwise it's not a unique story.
So you have to know your characters in context of your Setting, because that will shape them.
I use the following questions to guide and focus my pre-pre-production work. And it will be a lot of work. But it's information you should know, like the iceberg metaphor used earlier.
How do my Characters make a Living?
This is the epitome of Expectations = Results. It's the day to day life.
To get into a character we must question all aspects of their 24 hour days. How do they sleep, play, pray, work, make love, eat? etc.(edited)
What are the Politics of my world?
Politics is Power.
Who orchestrates the power in your tory's level of society?
In any organized set of people there is an uneven distribution of Power.
What are the rituals of my world?
The conventional ways of doing things, private and public.
Cyclical in nature.
Each character may have things they do on a regular basis or that society does on a regular basis.
What are the Values of my World?
What do my characters consider good/evil, right/wrong?
What are society's laws?
What is worth living for?
Foolish to pursue?
What would they give their lives for? {I personally find this the most insightful}
What is the Genre or combination of genres?
Knowing this will help you know your conventions of the Genre so you can make or break them.
Conventions are also known as cliches. So to avoid cliche identify what categories your story fits into and study what other similar stories have done with their plot and world.
What are the Biographies of my Characters?
From the day they're born to the opening scene, how has life shaped them?
What is the Backstory
Different from Bio.
It's not life history but the set of significant events that occurred in the character's past that the writer can use to build the story's progressions.
We don't bring characters out from a void.
We landscape the character bios, planting them with the events that become a garden from which we can harvest again and again as the story needs.
What is the Cast Design?
Nothing in a work of art is there by accident.
Ideas may be spontaneous , but we weave them consciously and creatively into the whole.
Each role fits a purpose and the first principle of the cast is Polarization.
Between a variety of roles we devise a network of contrasting or contradictory attitudes.
No two Characters should react identically.
After this starting point you will know what other questions to ask of the story to get a better grasp of the world that you need to know in order to tell a tale that does not fall into repetition or cliche.