Folder structure

Rules of thumb:

For simple applications:
- Keep all components under ./src/components
- Create a directory for each component, and put all files for the component in that folder. For example, if you're creating MyComponent.js, it should be stored as such:

src
  components/
    my-component/              // kebab-case for directory
      MyComponent.js           // TitleCase for js/css files
      MyComponent.test.js
      MyComponent.css

For more complicated and bigger applications, you can structure your directories according to features or routes. Components which are shared across features can be pulled up to a common utils/ folder

Example:

src/
  common/
    Avatar.js
    Avatar.css
    APIUtils.js
    APIUtils.test.js
  feed/
    index.js
    Feed.js
    Feed.css
    FeedStory.js
    FeedStory.test.js
    FeedAPI.js
  profile/
    index.js
    Profile.js
    ProfileHeader.js
    ProfileHeader.css
    ProfileAPI.js

Further reading: https://reactjs.org/docs/faq-structure.html