Below I link to a variety of useful sources of advice to graduate students in philosophy, including prospective graduate students. As I am not aware of such collections elsewhere, I am hoping people might add to this list so folks know where to look to find advice.
Tips for applying to graduate school (Alex Guerrero):
Should you pursue graduate study? (Rutgers Philosophy):
https://philosophy.rutgers.edu/should-you-pursue-graduate-study-345
Advice About Applying to Ph.D. Programs in Philosophy (University of Mississippi Philosophy):
https://philosophy.olemiss.edu/a-guide-for-philosophy-graduate-students/
Graduate School Advice for Philosophy Majors (Humboldt Philosophy Dept):
https://philosophy.humboldt.edu/phil-grad-advice
Applying to PhD Programs in Philosophy, Part 1: Should you apply and where (Eric Schwitzgebel):
http://schwitzsplinters.blogspot.com/2019/06/applying-to-phd-programs-in-philosophy.html
How to be an awesome first year grad student (Eric Schwitzgebel):
12 Tips for Success in Philosophy Graduate School (Liz Jackson):
http://liz-jackson.com/wp-content/uploads/2020/07/12-tips-for-philosophy-grad-school.pdf
Advice for the philosophy job market (Dan Korman):
https://korman.faculty.philosophy.ucsb.edu/jobmarket.pdf
A safe and supportive forum for early-career philosophers:
Maintaining Sense of Confidence and Self-Worth in the Face of Failure and Rejection (Lisa Miracchi):
Self-Compassionate Writing Exercises (Lisa Miracchi):
Advice for Succeeding in Graduate School (Stanford Philosophy):
Some additional resources:
https://dailynous.com/2014/08/21/grad-traps-guest-post-by-daniel-silvermint/
https://dailynous.com/2020/09/28/douglas-portmores-six-commandments-getting-graduate-school/
https://dailynous.com/2019/03/28/transformative-experience-graduate-study-philosophy-paul-quiggin/
Turns out that Adam Patterson has a great collection of such advice on his web page here: https://adamfpatterson.weebly.com/resources.html