One possible version:
Dear Li Hua,
I’m very glad to become your classmate．I know you are worried about your study and don’t know how to adapt yourself to the new environment．There are some suggestions about it and I hope they can help you．
You know we always become puzzled when we go to a new environment because we don’t know anything about the people around us and even don’t know what to do．I think you should make friends with the students in our class．Then if you have any problem you can ask us or our teachers for help．We’ll try our best to help you．
After class, I’ll show you around our school and tell you something about it．If you have any problem, please tell me and I will give you my advice not only on study but also on your life here．
All in all, I hope you can adapt yourself to the new environment and we can become good friends．
Best regards,
Yours,
Li Yue
认真审题，分三段写作：1.帮他分析原因； 2给他提出建议； 3.陈述你帮助他的具体打算。注意过渡要自然，书写要认真。