What should I do to prepare before moving to Germany and settling there permanently?

I am currently a 7th-grade student in Vietnam. I have not learned German yet, and I am planning to move to Germany next year. I learn foreign languages quite quickly and can absorb new knowledge well. What should I do to be able to integrate into the community and enroll in a Realschule  or Gymnasium as soon as possible after arriving in Germany? I am planning to settle in Berlin. Should I study anything in advance before moving there? Are the subjects taught there difficult? What challenges might I face as an international student, and how can I prepare for them? (English isn’t my first language either ,so I’m sorry if there were any spelling mistakes )