Start without using scenes. Try to keep you whole game in a single file.

Add in primitive objects (ideally Shapes).

Sketch in behavior using Tags and built in functions.

Add in IMGUI windows to test out functionality.

Add in Tweens to find a game feel.

Create object types and convert most-used tags to fields. Add in object functions where necesasry to encapsulate common object operations.

Starting splitting out objects into Scenes.

Add in scene transitions between scenes.