Although writing is an art not a science, there are a few structures that writers have created over the years to assist in story creation. You may have even been using the Three Act Structure without even knowing about it.
In total the first act should only be about 1/4 the story, introduce many of the main characters and set the main character forth on some sort of adventure.
Act one should begin introducing the main character. He should be in his status quo, or everyday life, showing one of his strengths and weakness. One example of this is in the Hunger Games, Katnis is using her bow to hunt food. Then the story should introducing some side characters. Then about 1/8 into the story, there should be an event that disrupts the main characters status quo, such as a dragon attacking his village, that changes his life forever. He should then be presented with an adventure, such as joining a group of soldiers to go fight the dragon, however the main character often at first resists going on the adventure, they always end up going. And them going on the adventure marks the end of the first act.
Honestly Act 2 is the easiest act. You just need to move your characters from act 1 to their object in act 3. You'll want to add plot twists and thickeners to add some interest and make it seem like the main character will never reach his object so that it is much more satisfying when he does.
Act three is considered the Resolution. It's where the climax happens, the final battle, but it also includes the aftermath of the climax. It often has a different mood than the rest of the movie. An important thing to try to do in Act Three is to make the Main Character change in some way.
Zachary Will is an Award-Winning Filmmaker creating short films and content for the Internet as the owner of Riverside Studios. He has a Bachelor's in Film from Full Sail University. He has worked on productions for companies like Webmd, Sears, Home Depot, Six Flags and more!
"the trick is to never give up... I think the secret of success is not how little you get knocked down but how often you get back up." - Gareth Edwards