Hi, i think for Vajrayana path, teacher is very important.
But this question is very wide and difficult to answer...
I can only comment from i observed in Singapore context.
Obviously, it is very important you find a teacher with very
good knowledge of whatever practice in Vajrayana you want to learn.
teachers have different specialties. But this is often
overlooked. The student is overwhelmed by charisma,
publicity, and other public relation characteristics...
This teacher should be able to communicate with you in your
language, and he should be reasonably accessible for any queries.
your main teacher will have the kind of 'yuan' with you that
you feel at ease with him/her and a genuine relationship can build
up.
The teacher should be interested in your development, not only
in how you will contribute to his/her activities. Though
these 2 kinds of motivation are sometimes mixed up in various
degrees and difficult to discern. He should have time and
patience and interest in you & your questions to a reasonable
extent. I say reasonable, because sometimes students have so
many neuroses that it is good to cut them off :-)
If you are looking to practice Dzogchen, the teacher must be
realised. It is impossible for the blind to lead the blind.
Don't hurry to call a teacher 'root Guru', because this is not
something one chooses really. The teacher who gives you the
greatest, the most ultimate benefit, that one automatically becomes
your root Guru.
There are also 2 camps of thinking. One camp says that you
should just stick to one Guru till the end. The other one
says that you should be open and learn from many Gurus. Each has
pros and cons. I think that for anyone beginning Vajrayana,
you should choose the open option first because it expands your
horizons.
Each teacher comes with a style of teaching, some tend to be
more on the intellectual side, some more on the practical side.
Some more traditional, some more free-style... So the teacher
you choose depends on which style you are more comfortable with.
The teacher should be looking to make you more and more
independent and self-equipped with all the knowledges, skills and
confidence to go on the spiritual path yourself. You should
not be more and more dependent on the teacher as some kind of
crutches (emotional or otherwise)
You can also take a look at how the closer long-time disciples
of the teacher are doing... if you like how they are turning out,
then it may also be a good sign that the teacher is doing a good
job.
Besides assessing the teacher, one should also assess oneself,
your own motivation and see what is it exactly one is after. If you
understand yourself well, i feel that more or less, one will have
alot more clarity to choose a proper teacher.
Actually, this teacher-choosing thing is very difficult to
define as there is such a wide variety of situations. What i
said is just what came to my mind impromptu. It is a matter
of your conditions and merits. I would suggest that anyone
who wants to get a good teacher, makes strong prayers to Buddhas
and Bodhisattvas to guide them towards a genuine master and
accumulate merits. They should also start by learning as much
as possible about Vajrayana. There are alot of introductory books
out there already.