To achieve the state of d’veikut (attachment to Hashem) as practiced by the Baal Shem Tov, one strives to attain the state of bitul ha’yesh (the nullification of somethingness).
In this state, there is an awareness that Hashem alone is true reality and that all finite things are dissolved in His unity. In the state of bitul ha’yesh, the soul can soar to Hashem while the ego is left behind.
This state is especially to be cultivated at the time of prayer. Thus, Hasidic prayer is essentially an exercise in forsaking the world and abandoning the lower self.
Adapted from Heart of Prayer: Baal Shem Tov