Get your main character (protagonist) up a tree.
Setup the world they live in. What's their life and situation like?
What do they need and want as the main character? Give them a problem and a difficult choice that takes them into the second act. What will the consequences be if they do or don't take up the challenge in front of them?
Throw lots and lots of stones and rocks at them.
Plenty of obstacles and hurdles that they must overcome as they make their way through the story.
Making the right and wrong choices along the way.
What, or who is standing in the way of them achieving their goals?
Get them down from the tree.
What do they need to overcome, both internally and externally to get them to the end of the story?
What have they learned about themselves?
Do they have a character arc by the end of the story?
How is their life now compared to the start of the story?
Is it opposite to how they started out?