Think about a faculty member in the building who knows you on a personal level. You want to ask the person who knows you well. This could be a teacher, a counselor, a coach, a sponsor, or someone else you worked closely with. You want them to speak to your personal qualities, and not just about your academics.
Make sure to plan ahead! In order for the person to write a strong letter, you want to give them at least two weeks (minimum) to prepare it.
Ask them in person. Writing a letter takes time, and it is polite to ask the person face to face if they are willing to write one for you. Do not be offended if someone says no, it is probably for the best as they may not have time to devote to a strong letter.
Gather appropriate documents to help the person writing the letter. The recommender should be able to know exactly how they should prepare it and where to send it once it is written. If you need a letter of recommendation for a college application, fill out the brag sheet in your Schoolinks account. You will be able to send this brag sheet to the person writing your letter via SchooLinks. Some schools or scholarships want it sent directly from the writer without the student having access to the letter. If this is the case, make sure you know who and where the letter needs to be sent. Make sure to be very clear about the deadline as well.
Stay in touch with your recommender. Make sure you check in with them prior to the deadline to remind them. Once they have submitted it, send them a thank-you note expressing your gratitude and appreciation.
Reach out to your counselor with any questions about this process.