One of the nice things about using a dedicated screenwriting program is that it helps you type less of the things you need to type a lot. Fountain Mode provides autocompletion for scene headings and character names.
The completion candidates are not updated automatically so you need to
call fountain-completion-update to update them. You’ll probably
do this more while writing the first draft of your script, when you’re
still adding locations and characters. For convenience you can add
this command to fountain-mode-hook so it gets run whenever you
open a script. See (emacs)Hooks
This command, bound to C-c C-x a will update the completion candidates for current buffer.