There are many decisions that you can make to improve the quality of your codebase. There is no a recipe that you can follow because each application is different but there are some general things that can make your life easier.

Here are some tips that helped me a lot:

- Keep your solution and tech-stack as simple as possible

- Mark those parts that can change often and try to make them configurable (when you have it configurable you don't need to change code and re-deploy every single adjustment)

- Make sure you have a good and readable logging

- Use DI

- Separate your application core application logic from the infrastructure part (DAL, Network Communication, Log Provider, File readers/parsers and similar)

- Keep your functions/methods clean and without side effects

- Method has to return something (try to minimize the usage of "void" methods)

- Split each feature or functionality you are working on into small pieces and compose the final thing with them

- Be disciplined about your naming conventions and code style