Submit the number of recommendations that is requested.
Select academic/professional references, not personal/social ones, including:
- research advisors
- summer program mentor
- undergraduate academic advisors
Ask the recommenders to meet with you beforehand, if possible.
Give your recommenders a copy of your personal statement and CV so that they know what your plans are.
Emphasize to recommenders how important a strong letter of recommendation is to your application
Give them as much time as possible so they can write a substantive letter.
Follow-up with the schools and the recommenders before the deadline, to make sure that the letters were submitted and received.