Here are some guidelines to help you when approaching a faculty member for a letter of recommendation.
1. Ask a professor who knows you.
Recommendations are usually based on either your work in a course or knowledge of your character or abilities through extracurricular activities. It is not based upon seeing the professor in the hallways and saying hello on a regular basis. Therefore, you should ask a professor who can attest to the quality of your work in a course or your accomplishments.
One student asked me for a recommendation two weeks into the semester. I politely declined because she was an unknown quantity to me. I also let her know that anyone reading the letter would clearly see that I had nothing upon which to base my recommendation. I suggested she ask another professor, one who could genuinely endorse her and her work.
2. Assess whether the professor’s knowledge of you is overwhelming positive.
The answer to this question must be a resounding, “Yes.” And how do you know that the knowledge is positive? One clue is how you did in the professor’s course.