I found the following notes on how to find a good mentor. I think this also gives hints on how to be a good mentor from a different perspective. In other words it shows what type of mentors the students look for.

The tips are summarized as follows:

Ask yourself what you want in a mentor or sponsor
Check your employer’s human resources department to see if they have a mentoring program
Look outside the office
Do an Advanced People Search on LinkedIn
Consider a mentor younger than you
Practice your “Why Me” speech
Steer clear of the formal request
Show them how to help
Make it fun
Do something for them
Be a mentor
Listen