写感谢信时，可以遵循以下结构和要点：

开头问候

亲爱的[收信人姓名]，你好吗？我写信是想表达我真诚的感谢。

表达感谢的目的

简要说明写信的目的，例如感谢对方在某方面的帮助或支持。

详细描述帮助内容

具体说明对方是如何帮助你的，可以详细描述他们的行为、建议或提供的资源。

表达感激之情

用诚挚的语言表达你对对方帮助的感激之情，可以提到这些帮助对你的重要性。

未来的承诺

如果适当，可以提到你打算如何回报对方的帮助，或者你将继续努力学习或工作以不辜负对方的期望。

结束语和签名

用“Yours truly”或“Best regards”等结束语，并签上自己的名字。

```

Dear [收信人姓名],

I hope this letter finds you well. I am writing to express my sincere thanks for [具体帮助或支持]。

Firstly, you helped me understand the difficult grammar points, which was crucial for my recent exam preparation. Secondly, your guidance on [具体事项] was instrumental in helping me overcome my challenges. Your patience and expertise were truly invaluable.

I am deeply grateful for your support and the time you have taken to help me. It has made a significant difference in my life and I am confident that with your continued guidance, I will achieve even greater success.

Thank you once again for everything you have done. I look forward to the opportunity to repay your kindness and learn from you in the future.

Yours truly,

[你的名字]

```

希望这个示例能帮助你写出一篇优秀的感谢信。如果有更多具体情境或细节需要添加，请随时告诉我。