Ask HN: Career development advice for junior developer?

Developer friends of the magical Hacker News! If you've worked for more than a year as a software engineer, what would you suggest as a goal for technical skills and personal growth for someone just starting their tech career to strive for, and what was the one thing that you wish you had done in the first year of your career?

(The stack I currently work with is Python, Django, Django REST Framework, React, React Native, PostgreSQL. I am interested in learning more about web security, SQL performance, and can pick up any technology that will help solve problems. )