If you have the time, defer things with TODOs. Yes, that's the path to tech debt, that's why I started with "if...".
Write tests, positive and negative, before (TDD), meanwhile and after. As many as you can think of without straining. Real life will provide you with more. Integration tests, for each layers if possible.
Start writing with comments and or pseudocode. If the latter and your programming language is #Python, you're halfway there.