Letters of recommendation, as you may know, have many implications. Among those are scholarships, job references, and in the college application process. A good place to start when considering a person who can write a letter of recommendation for you is by thinking about your relationship with teachers, coaches, employers, and faculty. If you do not already have a person who can speak well about about your strengths, it is not too late to start building a relationship with the person who you may want to receive a letter of recommendation from.
When I was looking for teachers who could write a letter of recommendation for me, I started by thinking about the organizations that I was a part of. Then I thought about my role in the organization. Once I had about 3-4 teachers that I felt comfortable reaching out to, I approached them in person and talked to them about where I was on my college application process. An in important thing to keep in mind is that the more time you give the person writing the letter, the more likely it will be that they can write a letter that speaks to who you are as a student. You must also keep in mind that sometimes when you ask, the person might not feel like they can write a strong letter of recommendation. In this case you should thank them for considering your request, and you should find another person who can help you write one.
I would argue that the key to asking for a letter of recommendation is timing. It is important to ask about a month and a half in advanced. At the end when you receive a letter from the recommender, you must remember to show your gratitude. A simple way to do this is by writing a thank you letter.