In my twelve years in ministry, there have been a few folks who have decided to invest in me and speak into my life. I'm much better because they took me under their wing and helped me when I needed good counsel. Sometimes I knew I needed help, but a few times they would reach out to me when I was in trouble and didn't even know it.
Everyone, in my opinion, ought to have one or two of these folks in their life. Senior Pastors, especially, need a mentor or two. But I would make the case that this applies to everyone.
I'm not a big fan of making this 'formal'. There is a school of thought that says you have to negotiate a mentoring relationship, spell out expectations and time limits. I prefer to let this happen naturally. Over time, as you build friendships, it becomes obvious who is around you who can mentor you. You don't always have to name it, but I know who's mentoring me and I know who I'm mentoring.
Who's speaking wisdom and truth and care on a personal level into your life?