Dear Sir or Madam,
This is ----(你的名字)，the purpose for me to write the letter is that there is some issues when I expect to --- (去干什么). The situation is that I need to score well to enter---(要申請的); however, I have difficulty to complete ---（有問題的）.
As I learned that you are outstanding in the field of…(具體的方面). Also, you are the most qualified person for me to turn to. I am appreciated if you could provide with certain suggestion or information, and it could help me a lot. In addition, I apologize to take your cherish time.
I sincerely expect you could reply me with any suggestions. I am looking forward to have some opportunities to improve myself under your guidance.