You can ask for a letter of recommendation by writing an email to the professor, using Deadr.xx (preferably the title in his email automatic reply), beginning with who you are and what class you are in. Use simple and polite language and never make low-level grammatical mistakes or spelling mistakes. Please ask the professor to write a letter of recommendation at least two weeks in advance, so as to leave him enough time. The best time to ask for a letter of recommendation is after completing a course or thesis. Please pay attention to your attitude when writing letters of recommendation. Don't think the professor is obligated to write you a recommendation letter. If the letter is written like this, it will also make the professor happy: I will be happy to provide you with any documents or materials that will help you write a solid letter. Please let me know what you need. This can avoid the embarrassment that the professor can't write a recommendation letter because he doesn't know you. In short, it's never wrong to get along well with professors! Whether applying for a doctorate or looking for a job, you should maintain a good and harmonious relationship with the professor.