There are many ways to help:
- Help them develop their research interests.
- Help them identify potential advisors.
- Provide structure and guidance on how to write their research statements.
- Write an informative letter of recommendation.
- Ensure the the research projects they participate on give them an opportunity to contribute meaningfully, so they have substantial experiences they can write about.
- If appropriate, help them apply to the NSF Graduate Research Fellowship Program (GRFP) . This can help with the above, developing interests, and informing research statements. (Remember that NSF GRFP statements should be primarily developed by the student, not you).