Having mentored many startups, I find this article very true.
Be Specific: Whether you are looking for someone who can guide you better on your Marketing skills, or for someone who can coach you on the latest PHPskills, you need to be specific with your requirements. You also need to mention very clearly where you see the need of a mentor to step in. Remember, mentors are pretty busy. They do not have time to read through your mails. They’d like to see what’s in for them and HOW can they help.