How to ask for a letter of recommendation
Ask in person -- this gives the recommender a chance to chat with you about your interests and why you’re pursuing the award.
Provide specific information about the scholarship program, any forms required, and a copy of your advising report. You may also want to provide a copy of your resume or a paper you wrote for the class you took with the professor.
In almost all cases, you should waive your right to read the letters. Some scholarship organizations require this, and most scholarship evaluators prefer the candor of confidential letters.
At the same time, do seek people with the appropriate rank. Usually fellowship committees are not impressed by letters from high school teachers.
Pay attention to scholarship guidelines. Some awards (Goldwater) will only want faculty recommenders. Other awards like to see letters from members of the community or people who’ve supervised you in a workplace setting.
For your recommenders to write great letters, they have to get to know you. In small classes, your participation in class might be enough, but in most cases you have to go the extra step of developing a relationship with them outside of the classroom.
Visit office hours, attend departmental lectures and events, and make it a habit to follow up. Ask if you can get involved with research with your professors.
If the potential recommender is a supervisor from some co-curricular activity, stay in touch with them, and make it a habit to follow up with them about relevant experiences and events.