In general, you should ideally ask for a letter that can
substantially bring an added value to your application package,
and communicate information that cannot be directly inferred from
the rest of your application materials. For example, if I have no
more to say than the fact that you have done a good job in a
course and have obtained an A+, that wouldn't say much, since this
information is already apparent from your academic transcript. If
you're applying for a Ph.D. program, your letters should ideally
come from those who can comment about your research track record
and potentials, and this information can only be provided by
someone who has supervised a research project done by you. For
more information on the best practices regarding letters of
recommendations, and graduate applications in general, read the amazing
advice by Professor Mor Harchol-Balter at CMU. I myself
benefited from this guide back when I was looking for Ph.D.
programs. Best of luck for your search!
(Disclaimer: This
is my personal website, and any opinions expressed in this
website are solely my own.)
Last Updated: September 2022