Mentoring is one of the most important factors in your own advancement. And one of the most accessible, because you can find it for yourself.
I re-discovered this article recently that compares formal mentoring to informal mentoring, with a surprising win for informal mentoring. Why? Well, informal mentoring relationships generally start spontaneously, and mean that the mentor and the mentoree get along well, and have similar interests and values. Another benefit is that naturally compatible mentor and the mentoree relationships enable stronger communication and they will be able to better share ideas, feedback and challenges.
For further information on why mentoring is worth doing, how informal mentoring relationships start and why they work, read the full article.