First seeker must inquire into the nature of the physical body i.e. matter. Second he must inquire into the nature of the mind.

There is no practice as such but perfect understanding is needed.   Deeper inquiry, analysis and reasoning revels the fact that, the self is not physical but the self is formless consciousness. Therefore, all the accumulated knowledge, experiences and understanding based on physical self [ego or body as Self] are falsehood based on the false self, within the false experience (waking).   Thus, whatever is based on the waking entity is bound to be falsehood because waking experience itself is false hood.   Since many teachers and teachings are based on the false self (ego or waking entity) and they consider the false experience (three states) as reality, they are incapable of grasping the witness, which is within the three states, but it is without the three states.

 First seeker   must inquire into the nature of the physical body i.e. matter. Second he must inquire into the nature of the mind. 

Observe at everything in nature because in everything there is consciousness. One should not avoid them, do not shut his himself to Nature; and he should not shut himself away from the world which is as much consciousness, as anything else because the consciousness is the cause of  the three states and it itself is uncaused. 

To say this world is illusion without first examining them and inquiring into them thoroughly is to delude yourself. The world is reality within the waking experience. Same way as the dream world was reality within the dream.   

The person, who stamped their foot on the ground to refute to show the world, is real, ignore that in dream he would do exactly the same--stamp his dream foot on the ground and assert it to be real. 

The dream becomes unreal when waking takes place. Similarly the waking becomes unreal when wisdom dawns. Wisdom dawns, when the waking entity indulges itself in deeper self-search and realizes the fact that, it itself is not the self. But the self is the formless witness of the three states.  The formless witness of the three states is the soul or consciousness, the innermost self.   Formless Consciousness also is the substance of the three states. Thus formless witness and substance of the three states are one in essence. Thus there is no second thing exists other than consciousness.   Thus formless consciousness (soul) is ultimate truth or Brahman.  Thus on the standpoint of the soul, the innermost self, all the three states are mere illusion. Whatever prevails without the illusion is ultimate reality or Brahman.