If you don't ask your chaa-wala to recommend nail-artists, don't ask a professor of linguistics to recommend a potential Aeronautical Engineer. This is just for the sake of credibility. To relate your insights over a non-credit course to the degree you aim for is a hassle for both the student and the faculty in question. It's recommended to go to well-referenced faculty members of your preferred major.
Equip your teacher with context so that he/she is well aware of your target. They may choose to start on your letter a week after you asked, so he/she might forget which schools you plan to apply to or which of your qualities you would want highlighted. Make a document with your “Preferred Universities” list, list of deadlines, a personal statement and CV, and send it to them with your request.
Leave them alone
A week to write a recommendation letter on a student they possibly taught 2 semesters ago is not enough. Don't give them a week and expect something better than essays written off of a template on the internet. If they give you half a semester to write a paper without plagiarising, you can give them a few weeks to write something that could make your career. During that period, do not rush them. Only gentle reminders are okay.
Susmita is a literature major who lives on tea and sweet toast. Reach her at email@example.com.