There is conscious and unconscious. There is nothing called subconsciousness.
There are two files in our mind. One is temporuary memory and other one is permanent memory.
Whatever you want remember for the time being, it will be recorded in temporuary memory and those you want to have remembered always is stored in permanent memory. This permanent one is called subconscious mind.
In the conscious mind it decides whether one act is good or bad.
Whereas all the strong desires that we wanted to attain unconsciously or consciously goes into the subconscious mind, but it has no capacity to differentiate between good and bad.
It will try to do whatever you have put in subconscious mind.
A normal person cannot control over it.
This subconscious mind is connected with superconscious or universal mind where all thoughts of all human being are recorded.
Say you want to realise god, you go on repeat thinking about it, then it goes to subconscious mind, it starts acting according your wish and search for all the possibility of finding a guru or master to help you. You need not to do anything.
That is why repetition of some mantra with particular purpose is prescribed in Hinduism.
How to control this subconscious mind.
First we shoould have a calm mind through meditation, pooja, Bhajans.
Next watch your mind continously & consciously without getting attached to it.
This is called cleansing your mind.
Whatever you have accumulated in this life and previous lives will come out. You will know what are all thoughts to be retained and cleared.
Slowly your subconscious mind will be empty or with very few good thoughts.
Now you have controlled the subconcious mind.
In this stage whatever you wanted to do it will be done immediately. Here all the miracles starts happening.
Still we have to go long away to realise god.