TypeScript

avoid any; get rid of any existing any whenever you can so that we can enable "strict": true later on in tsconfig.json
define custom types for common data structures
- don't worry about interface vs type, both are fine

Typescript and React/Next

use React.FC<Props> type for React components, e.g. const MyComponent: React.FC<Props> = ({ ... }) => { ... };
use NextPage<Props> for typing stuff in src/pages/
use generic versions of GetServerSideProps<Props> and GetStaticProps<Props>

React

create one file per one component (tiny helper components in the same file are fine)
name file identically to the component it describes (e.g. const DisplayQuestions: React.FC<Props> = ... in DisplayQuestions.ts)
use named export instead of default export for all React components
- it's better for refactoring
- and it plays well with React.FC typing

Styles

use Tailwind
avoid positioning styles in components, position elements from the outside (e.g. with space-* or grid/flexbox)

General notes

use const instead of let whenever possible
set up prettier to format code on save