Letter requests are not automatically approved, you need to put effort in during the academic year in order to receive a good letter. If I don't know who you are, I won't write you a good letter. 

I will only write confidential letters - you must waive your right to view the letters when you apply for things. 

Make sure that you provide explicit details on the form about the purpose of the letter, the name of your program, and the date(s) that the letters are due. 

If you need multiple letters, you need to notify me further in advance than the normal one month