First, you have to understand the duality. It is the desire of Lord Shiva to enjoy this duality. Now, with its own grace, it goes beyond duality to enjoy non-duality.
So nothing wrong in duality and it should be enjoyed as leela. If you, because of grace of Lord Shiva want to move towards non-duality, you have to rise above body, mind identification.
Start from vismay-yoga-bhumika, be curious like a child who is filled with amazement.
See clearly, that every experience is made up of sight, sound, touch, smell, taste and thought. Nothing else.
Now, examine the source of all these senses and mind.
You should get an answer from your experience, not from a book. Once you get the answer you will slowly start establishing in non-duality.
The biggest impediment on this path, however, is your ego. Ego means- I am a woman, I am a mother sister daughter, I am beautiful-ugly, I am pious, I am intelligent, I have achieved this etc. All this must be eliminated.
What I mean is, whatever is dear to you as a person must be eliminated, if you want to get rid of ego.
Shiva says in Malinivijyottara-ego is the root of all ignorance. It is needed to create the world as you see.
But it must be eliminated to destroy the world. No ego- no ignorance. The destruction of the world here means, destruction of agyan or ignorance. Because the world as you experience is because of ignorance of your true self, your Shiva Swaroop.
This can be achieved through the succession of three upayas-
1. Anavopaya-e.g. chanting a mantra.
2. Shaktopaya- e.g. through mantra get one-pointedness and establish in thoughtlessness.
3. Shambhopaya- after thoughtlessness with your pure will to merge in Lord Shiva, the great lord will merge you into the ocean and you will feel I was never a drop but was always this ocean.
Undivided, undifferentiated, unmanifested, eternal, infinite, I am.
Om Namah Shivaye.