A mentor is person who can guide you in your career. A mentor will be called a 'good mentor' when he/she understand you and know how to make you understand. He/she should motivate you, guide you, assist you, like what you are doing and most important should be interested in what you are doing.

The opposite of above will be true for calling someone a 'bad mentor'. Besides that a mentor should not enforce his/her own ideas on people, instead he/she should shape the dreams of people in a way that they have wings and they can fly n reach the sky.

I have been mentoring and advising since years and I can tell you it's a relationship like love. I am always concerned about them and they are always concerned about me. We compliment each other and we think of growth on mutual terms.

You must have an interaction with the potential mentor/advisor and find out whether he/she is matching you or not.

All the best.
Shishir