In order to practice the yoga of discrimination (jnana yoga), it is necessary to have a highly developed mind. To strengthen yourself for the practice, it's necessary to learn to concentrate. Each day when you meditate, you should devote the first few minutes of your meditation to concentration.
If you practice a little jnana yoga in your daily life, it will help you tremendously. All you have to do is ask yourself one question whenever you are trying to decide what to do: "Is there truth in what I am doing now?"
Discrimination involves reflection. We have to constantly ask ourselves: "Who am I?" We have to remind ourselves that we are not the transitory body, we are not what we perceive with our senses, we are not the person who is having experiences, we are not affected by action or inaction.
If we really reflect and discriminate, we'll find that all things are created by our perception, that all states exist within the mind. When we erase perception, then we erase that which perceives perception. The universe dissolves and we see that it was never real to begin with.
On the path of discrimination, we examine everything in existence and come to see that things are transitory and temporal.
We find a way out of the transitory by realizing that there's no place to go, that there's no way out, that there's no way in. All that exists is the Self. The Self is eternal. You are that Self. Beyond words, thoughts, ideas, forms and belief systems. There is nothing but the Self. There is no world, there is no time, there is no place, no condition. There is nothing but eternity. Eternity has always been and will always be.
Discrimination means you know the difference between the transient and the eternal. That's what discrimination means in Shankara's yoga.
The yoga of discrimination is only truly practiced once you have started to go into Samadhi. It is only in Samadhi that you'll begin to get an inkling of who you are.
On the path of knowledge we view life as in a dream. We feel that this world is a dream. So when we wake from the ignorance of this world, the dream of existence, all of the experiences that we have ever had fall away. The ideas of life and death, of rebirth, of reincarnation, karma, God, truth, knowledge -- all these things fall away. All the concepts, all knowings, all truths, all religious systems, all beliefs, fall away in the white light of eternity. In that undifferentiated reality of the Self there is eternal bliss.