Preproduction stage help.

I can only speak from 3D animation point of view. 3D games are done differently, but I have a lot less experience with those. The best starting point is a screenplay AKA the script. Unlike live action, in 3D animation the writing of the script is part of the preproduction and not a separate process. That is way it is called Story Development. In Live action it is it's own separate process called Development. Different studios/people will have different order and pipelines. This is why it's so hard to find information on 3D animation production. So, my experience is with independent groups and art students in the Dallas Texas area. Others may have different pipelines.

The most common way I've seen it done is Start with a story idea. Then depending on your focus and the number of people working on Story Development you will do Character design(What they look like, why do they act the way they do, important background info, etc.) this can start with written Bio or drawing/modeling out your character. Character design is covered here: https://cgcookie.com/courses/character-design-process I personally prefer this one: https://cgcookie.com/courses/concept-create-concept-art-with-blender you will also want to create Character sheets AKA Turnarounds : https://cgcookie.com/courses/create-turnaround-modelsheet-blender. You may want to learn about grease pencil before you start the Concept or Turnaround course by watching DRAW: https://cgcookie.com/courses/grease-pencil-basics-an-introduction-to-blender-s-grease-pencil. In 3D animation, you usually jump straight to writing a Shooting script. I prefer to start with a spec script(Speculation Screenplay). The difference is that shooting script adds the camera work AKA Shots elements. It also adds Transition elements. For this you will need to know a lot of camera terms: https://cgcookie.com/courses/directing-the-camera-in-blender. As for the elements and formatting of script there isn't a CGC course yet. Note: I haven't watched the collabs that Omar pointed too so I don't know if that is covered in that. Here are 2 YouTube videos. I like the first one, but the second one covers more info, like story structure, which is better if you're more interested in the writing aspect.

https://www.youtube.com/watch?v=_2uZ7IabVOM

https://www.youtube.com/watch?v=4hepINkxlkc&list=TLPQMjIwMjIwMjVgoYr4oEYzBw&index=2

I also recommend looking into Fountain markdown. It allows you to write your screenplay in any text editor(Including Blender's) or word processor. As long as it can save plain text. Then you can use it. Then you use a formatting software to do all the formatting for you. You can goto https://fountain.io/ to read all about it. If you prefer to watch a video then https://www.youtube.com/watch?v=X3ZdiUqrZ1g&list=TLPQMjIwMjIwMjVgoYr4oEYzBw&index=3.  As for formatting software, I use 2 different ones. The main one I use is https://afterwriting.com/ You can use it directly from the website or you can click on source code and use that as a local version. Side note: I only had internet access on my phone for the longest time. So, I used the local version. The second is a Blender addon: https://github.com/tin2tin/Blender_Screenwriter The newer version works with 4.x and now includes formatted PDF Export thru the text editor. It also has tools for storyboarding, but I prefer Storypencil addon which can be downloaded and installed thru Blender's extension platform.(AKA extension section of preferences) You can also read more about it here: https://extensions.blender.org/add-ons/storypencil-storyboard-tools/. Speaking of storyboard, if you have clear visuals of scenes/shots you may want to start here. Most of the time the Storyboard is created after the script and a lot of concept art(Character design, set design, color palette, clothes & hair design, etc.), however sometimes it's done first or as part of the concept art. Usually it's done first if there is a clear visual story with no or little dialog. Then everything is fleshed out. If the screenplay is written before the concept art is finished then it's normal to do the storyboard as part of the concept art.

There are a few course on Environments AKA set design(Technically Environment is a section of set design). I haven't watched any yet, but this is the first one I plan to watch: https://cgcookie.com/courses/using-3d-for-environment-concepts another aspect that applies to all design(Character, Hair, makeup, environment, etc.) is Color( https://cgcookie.com/courses/the-color-course) , and Form(https://cgcookie.com/courses/shapes-forms-and-contrast). There is a better video on YouTube about color and color theory. I'll add it to this post if I can find it again. 

Well that should be enough to get you started down the rabbit hole known as Preproduction. 

Forgot I had this. From when I thought about doing my own YouTube channel. I have some PDFs and links on my website: https://blenderclassroom.com/download.php then click Screenplay 101. The Courier Prime font can be used in Blender's text editor. Go to preferences->interface->text rendering->click folder icon to the right of monospace font and select the Courier Prime font. Note: Unless they changed it both of the fountain formatting programs use this font. 

Thanks Dwayne, It's very important knowledge here!