After you join your thesis lab, your PI becomes your primary advisor and mentor. No advisor is perfect—nor is any student—so you need to be proactive in asking for and seeking out the advice that you need. You also need to sort through the advice that you get.
Successful mentoring relationships contribute to the creation of a stimulating environment and a dynamic of reciprocity that facilitates the personal and professional development of the faculty member and the student alike. A proactive approach is necessary. If your advisor is not looking after you in the way you need, then you need to look after them. One of the secrets of looking after your advisor is working out what your advisor wants—and what most advisors want is a student who comes to them with suggestions and solutions as well as problems, who gets things done, and who ultimately makes the job of advising easier. In business this is called "managing up."
Here are some great mentoring workshops offered to Biosciences students: