Project overview and structure
Before you start your project, you should consider how you intend to set it up and architect your project in the long term. Far too many developers have created problems for themselves by just diving in rather than designing the outline for the project at the start.
Your game and your assets are not the only things to consider when starting a fresh project. Sure, you can start importing assets, creating scripts, and getting things running; most Proof of Concept (POC) projects start this way. Once your project is of a sufficient size and you start expanding on your initial concept, you'll realize that you have issues with regard to picking up items and putting them together. Then, you will start devising new ways to organize your project and eventually find that it's an unmanageable mess; nevertheless, you will stride on, taking longer and longer to produce new content or add new features.
The best advice one can give is to think about your entire project and...