Stick to conventions
If you're performing a task as there's already a convention on how to do it, stick to it.
If the codebase follows a particular coding standard, use it.
If a project uses repository classes instead of interacting directly with a database, do that with your code too.
If you use a framework with a service container and uses dependency injection, do that instead of manually creating classes.
If you need additional functionality for a Drupal project and there's an established and well-known module that adds it, use it. Unless it doesn't meet your needs, in which case, document why that's the case and why you used a different module or wrote a custom implementation.
If you need to create a content listing page, use the Views module, which is a standard approach. If not, document why and then explore other solutions.
If you don't follow a convention, it will be harder for you or others to work on it in the future.
- Oliver
