The core of this sadhana is to give oneself to the Divine and let Her mould us the way She would want us to be. What this means is that we think of the Divine keeping Her at the centre of all our actions and offering them all to Her in the spirit of service to Her. The principle is to increasingly forget ourselves and think more and more of the Divine. Even to think of one’s progress is to get back into the ego-self. Our work is to aspire and leave the rest including our progress entirely in Her hands. It is indeed a leap of faith and requires great courage.
Of course, there are some fundamental experiences that indicate that one is growing along the right tracks. These are growing peace and equanimity, psychic discernment, aspiration for progress, urge to serve and to give oneself. Apart from these, there are many other experiences, some core, others peripheral, but it is best if they arise spontaneously and one does not maintain a great interest in them. Otherwise, there is a danger of the spiritual ego toppling the Yoga.
All these things are well described in great detail and from every angle in the writings of Sri Aurobindo and the Mother, especially Letters on Yoga.
About Savitri | B1C1-10 The Response of Earth (p.5)