In the coming three years, your school life will be challenging.

You should learn to learn in an organised way.

Firstly, ... Besides, ... Finally, ...

Personally, it really benefited me a lot to ...

It's important to learn how to ...

I suggest you take part in sports frequently, which are helpful to build up your bodies and enrich your school life.

I hope you will enjoy a colorful and fruitful life here.

That's all.

Thank you (for listening).

【参考范文】

　 Good morning, everyone! It is my honor to be here to share with you my opinions on what to learn in senior high school.

　　In the coming three years, your school life will be challenging. So firstly, you should learn to learn in an organised way. Personally, it really benefited me a lot to preview lessons, get actively involved in class, and review what had been taught after class. Besides, it's important to learn how to get along well with others. In school, I respected teachers and was friendly with classmates. In this way a pleasant atmosphere was created. Finally, I suggest you take part in sports frequently, which are helpful to build up your bodies and enrich your school life.

　　I hope you will enjoy a colorful and fruitful life here.

　　Thank you!