Remain in beginner's mind. Assume you know nothing each time you are faced with a new task. Of course, you do know something, and this latent knowledge means it's easier to pick it up. But there should be no categorization like "this is a bad code smell" or "this is the best way to do it".

This is especially important as a 20 year old programmer, where you learn a lot of good practices, which don't apply for some situations or have unseen costs. For example, in many situations, a O(n^2) solution might be as effective as a O(n) solution, especially when n is very small and O(n^2) might cost too much overhead. Or say, hosting on a CDN. Make it a habit to ask yourself each time, do I really need this?

You should still learn best practices wherever possible, but assess whether they're applicable.