In a model-driven engineering (MDE) approach, the key principles to consider before embarking on this development methodology are understanding your "why", knowing if your domain is easily definable with a metamodel, and considering how complex the generator will be. It's also essential to determine how much manual coding the generator can save, how frequently you'll use it, how easy it is to update your models, whether the metamodel needs to change frequently, and how often the generator will need to change. Additionally, organizational factors such as team onboarding and iterative development are crucial to the success of this approach. By understanding these principles and being aware of the limitations and overheads involved, you can make the most of MDE in your software projects.