The most important thing is to rely on a qualified Guru and to follow His instructions

 I mentioned earlier that [Guru is] someone who is able to point at one’s nature; someone, who is able to show you the path to the nature of the mind. And therefore, it is a very important person in one’s life, because for a Dharma practitioner, most important is to realize one’s own nature; and that has to go through teacher’s instructions and guru’s blessing. In the history of Buddhism and the stories of the great Masters or great Dharma practitioners [it is clear that] one of the most important thing for those great masters is to rely on a qualified guru and to follow the instructions of the guru correctly and exactly. We are Vajrayana practitioners, we should try to have a correct understanding, which comes from study and real investigation. [I said that] because sometimes people do not have enough foundation to have a good understanding, [and they] do something before having that foundation. Therefore, people sometimes make mistakes because there is not enough understanding. So, we need to study first and try to get the most important or essence of that practice and that lineage, or one’s own practice.

 Hungkar Dorje Rinpoche, “GURU YOGA – Guru Yoga from Longchen Nyingthik Lineage”