How to Write a Video Game Script

Writing a video game script offers a challenge that goes well beyond the normal realm of writing. But it is also something that can be tremendously rewarding in the scope of its creativity. Here are some guidelines and tips for writing a video game script.
Today's video games are based in complex worlds and they tell stories. No longer does a player simply advance through repetitive screens slaying goblins and ghouls in a quest toward the goal. A player now expects to progress through a world where there is a rich history and a plethora of decisions to be made. This adds to the complexity of writing a video game script and it also adds to the richness of the creativity involved.
The first thing you need to think about is that writing a video game script is that it is not the same as writing a movie script. The two processes are similar and you do write a movie like script for your video game but that is only part of the process. There is a whole host of accompanying materials that you need to write for your game script. Here is an overview of what you need to write and why.
Write An Executive overview of the story in prose
This is the most important part of your game script and this is what will sink or float your script. This overview has to tell a compelling and unique story and it should tell the complete story from the opening scene of the game through the major steps all the way to the completion of the game. An overview like this can be almost any size and it would be very easy for this to be ten written pages or more. Remember that today's video games are very complex and the stories can be very complex. This overview is also the most important part of the script. You would shop this to game developers to see if they are interested in developing it into a game.
Write a History and Background of the world
Video games are complete worlds and game designers need to know what the world is like and what kind of history it has. This will help the designers to visualize what the world will look like.
Create a Flowchart for the entire game
Your game is going to be very complex and there will be many decisions that the player will have to make and each decision opens up a whole new path for the player to take. Creating a flowchart is the best way to keep track of all the possible paths through the game.
Create sub-quests and write a prose overview of each quest
Sub quests can be simple or complex but each one is a story in itself and you must tell these stories.
Create character descriptions and bios for all the major characters in the game.
Game designers need a complete picture of the characters in the game. Many of the non-player characters you create will pop up time and time again. And their story is woven deeply into the fabric of your world. You need to describe this relationship in detail to the game designers.

Write interactions with non-player characters
Your game will probably involve interaction with non-player characters (NPC's). You should write out the dialogue and flowchart the choices the game player can make. These interactions are often critical to the story and they can take the player on very different paths toward the conclusion of the game.
Write Cut scenes
Cut Scenes are short animations or movies that come before or after major plot points in your story. A cut scene should always be written to enhance or describe the story. A cut scene is also a reward given to the player for achieving a major milestone in game play.
Writing the actual storyboard script
This is the final step in the whole video game script writing process and it is the most detailed. You do this step last because you need all the supporting materials to understand and describe this correctly. This part is very similar to that of a movie script. You progress through each scene of your story and you detail all the necessary information. Here is an example:
Scene 1:
Location: A dark cathedral with stained glass windows. An NPC is kneeling before a stone casket in the center of the main room
Music: background music of an organ playing introduces the scene but subsides
Characters: Main player, NPC named Thomas, seven were creatures
Player Goal: Discover the location of the underground lair
Action: Player must initiate discussion with Thomas, upon first contact we activate cut scene (1) where Thomas morphs into a were-creature and summons his were-minions. Main character must battle the were-minions then re-initiate discussion with Thomas.
Flowchart: No decisions made at this point: If battle is completed Thomas reveals the entrance to the underground lair and player advances to that level. If player is defeated in battle revert to death cut scene (11) and move to try again screen.
Notes: Player is locked in the cathedral and there is no exit. The only viable way out is to initiate contact with Thomas. Random were-creatures can be activated if player explores cathedral before talking with NPC.