A good mentor nurtures and helps the mentee or advisee. Sometimes mentors show up out of the blue, sometimes they are people you know whose guidance you suddenly need, and sometimes you have to seek out a mentor and ask them to guide you.
Here is a checklist for what a good mentor will do most of the time. You might find that different mentors offer different supports from this checklist.
Listens. The mentor listens to your concerns, your interests without judgment. They act as a sounding board, helping you figure out what you think/dream/desire by letting you think aloud while they reflect back.
Teaches the ropes. Sometimes, when you are new to a field of study, you need help navigating the path, knowing what steps you have to take, what challenges to expect and how to manage them. A mentor may warm you about potholes and provide specific advice for a particular situation.
Objectivity. The mentor will provide an objective viewpoint of the options you have in a particular situation. They will be realistic.
Networking. The mentor will help you build a network, introducing you to people who may help you further, nominating you for helpful opportunities. They may suggest other supports (books, experiences, people to pay attention to).
Respect. The mentor does not humiliate, abuse, or manipulate you, or set you up for such treatment from others. The mentor encourages openness and honesty in the relationship.
Thereness. A good mentor will be with you emotionally and cognitively, not preoccupied with their own issues. They will stay connected as long as you like, but anticipate that you will move on when you need/want to.
Makes amends. The mentor asks forgiveness when they hurt you. And they forgive you in return.
Patience. You may not know it at the time but the mentor shows patience with you as you learn the ropes in their area of expertise.
Storytelling. The mentor tells you stories about their experiences or those of others. Sometimes it may not be obvious why they tell you a particular story, but it will become clear later.
Encouragement. The mentor encourages you in your passions, your dreams in a realistic manner. They see your promise, your uniqueness. They point out your strengths and are gentle with your weaknesses.
Emboldening. A good mentor will help you build your courage to follow your dreams. They will stand back and let you find your creative approach to life. While they point to your path ahead, they offer a cocoon/womb as you pupate/gestate the self-confidence to move forward.