This excerpt, in part was taken from an article in the Artist Daily and I agree with it completely.

What
make a great instructor.

The first trait: the instructor's work has to not only
be technically sound but it also has to move you.

You can't learn from someone
who doesn't believe in their art but it's even more difficult if you don't believe in their art–at the
very least, you need to be interested enough to want to learn more about it.

The way an instructor teaches how to think makes a big
difference.

And most of
all, a great instructor whatever–shares
what they know.

This is the crux of finding great  instruction.

You want
someone who doesn't hold back and answers questions as well as offers
assessments openly and thoughtfully.

Share knowledge is the key for me…. sometimes Tutors share, other times, it's like pulling teeth.