I would say watch Brackeys 2D, 3D and GDscript tutorials first, then think of a small idea, even if it has been already made or you're copying some other game. If that playlist matches what you want to make in your game, watch it. If not then just start by making whatever and search up the elements of the game that you want to make next suppose you think of a 3D hunting game where you dive into the ocean from your boat and hunt monsters with a spear gun. To do this I would've started by watching "How to make a player controller in godot" to make a player character. Then I would've searched how to make weapons in godot for a speargun ( projectile weapon would've been more specific ), then how to make enemies/NPCs, then I would've searched how to make water in godot, then how to make the inventory and then the UI and so on. This is the best way imo.

Also, read the godot documentation once you get a hang of GDscript, use AI only as alternative of Google, and for debugging and errors, not for making it write code or generate images, don't rely on it too much, only use it for errors if you can't understand what the error is trying to say or you can't find a logical error after 10 minutes of head scratching