How to create and idea for film story

create an interesting idea
do thought-generating exercises. (brainstorm)
you don't need to make a story at the beginning

start new idea with anything:
a phrase, a person, an experience or a situation

make it exciting and inspiring to you to create a story.

Story building method 

• Take an hour to write your idea in one-sentence
  Write as many ideas until you have an inspiring idea.
  Try the idea generator online, but create your own!

http://www.seventhsanctum.com/generate.php?Genname=storygen

• Expand your sentence into a one page story
  have a start, conflicts and the ending.
• Write a summary of the characters of the story.Start with main character and sub characters
• Expand the character with details.
  Write everything about each character.
  
  Make a synopsis from your work.
• Make a list of scenes of your story as a list.
• Describe each scene 
  place, time, people involved, happenings.
• Write your script now
  dialog and camera shots
• Create Your Storyboard

What is one an mind is only an idea.It becomes a story when you have written it.

The most important element in a story
is about characters and conflict.
Let's think of a story of a girl strugglling to gain freedom.
Now ask yourself questions to create her character with a conflict.

• Who is she? 
• What does she want? 
• What is obstructing her getting what she want? 

Character + conflict = story idea.Write that idea down.
Now transform your idea into a story plot.

Oh! now you face the hard part.
How to transform your high-level idea to a real story?
How do you turn it into a good plot?

The best is to start with the ending first. 

Ask your self; What happens to our girl at the end?

Think about your characters in deep,
associate them in your mind.
Virtually read their secret diaries.

What are their outer looks?
dark or fair? tall or short? modern or traditional?
likes and dislikes ? values and restrictions? skills and hobbies?
who are their associates (friends, families)
what are their hidden secrets?
What are their life experiences, needs, and desires.

Building the plot points

Take your characters and put them together
and see how they would interact with each other.

Create Friends, enemies, mentors, betrayers, saviors

Create incidents 
The girl impress everyone in a music competition but looses due to favourism.

Arrange your plot points into a story arc.


A 5 part model for a story:

Exposition
Shows the the normal life of the the character
until an "inciting incident" that creates a conflict.
The girl's home and school life shown.
She is not allowed to go on a trip with class

Rising Action
The character faces conflicts, struggles, and pitfalls
while trying to pursue their goals.
The girl fights to get freedom, but no result

ClimaxThe conflict comes to highest point at this point. 
At this point all seems possible or impossible.
The charater must must decide whether to go for it or fail and loose.
The girl desides to take part in a music competition.

Falling ActionThings start unfolding after the climax, the character wins or loses.
She looses the competition, but her song becomes a global hit

DenouementThe character begins a new life,
her family accepts their fault and get together again.
It could be another way also.
It's upto you to create the ending.

Work forward and backward.
Never afraid to change around or redevelop your plot.

More
http://www.teachingideas.co.uk/english/createa.htm