Luis, great topic!
I agree with you in that mentors can make so much of a difference in your career. Since they can sometimes be hard to find, once you have them, make sure to hold on them tight! They can be so valuable for your profession and progress.
In my opinion, a fruitful mentor/mentee relationship hinges on frequent communication and encouragement from the mentor side for the mentee's advancement. If the mentor/mentee relationship occurs directly within the work environment, there would most probably be an almost daily communication and touching on conversation topics related to day-to-day tasks. A relationship in which the mentor is outside of the mentee's work environment, from my experience, will touch on other peripheral and more broad topics that can be useful for the mentee's career.
In short, whatever type of relationship you might have, it is important to touch base frequently and make sure your mentor is aware of your goals so the best guidance can be provided. And don't forget, mentors also always have something to learn from mentees! So it is a two way relationship.
Hope this is helpful for the community.
------------------------------
Salvador Bentolila P.E., ENV SP, M.ASCE
AECOM
New York NY
------------------------------