Like you, you must be a very hard-working child to borrow your sister's book to preview before school starts, and you should be able to learn well because of your sister's advice.
When studying physics, you should read more books, ask more questions and do more work. Physics is a highly experimental subject. You should not only watch the teacher do various demonstration experiments carefully, but also do many experiments yourself. Some experiments can be done simply at home. I suggest you find some popular physics books to improve your understanding and interest in physics. Don't mechanically recite definitions, formulas and formulas to solve problems.
Chemistry is similar, but there are many things in chemistry that must be memorized, such as the top 20 elements in the table and the sequence table of metal activities. Relatively speaking, in mathematics and physics, chemistry is the best to learn.
Your question' learn physics and chemistry well?' This problem is really big. I can only give a brief answer. I hope it will help you a little.