yoga sutra (1:2) 

"Yogas Chitta vriti nirodhah"

In this sutra Maharishi Patanjali gives us the definition of yoga. "Yoga is the Stoppage of fluctuations  of mind". In this sutra "chitta" means our internal mind which is made up of 17 components, 5 jnanendriyas, 5 karmendriyas, 5 pranas, ego and mind. Chitta is all the mind stuff we gather and "vriti" means some modifications some changes fluctuations of the mind. Vritis are thoughts waves that continuously arises in our mind. 

Chitta job is to concentrate but due to this vritis our mind get distracted. whenever we try to sit for meditation & try to concentrate these vriti become obstacle, we think of the things other than the one we are trying to Concentrate.

"Give your mind something good to do or else it will find something worst to do"

When mind has no job then thought are Coming just without any purpose which waste our time and energy. We cannot stop the mind from  thinking but we can manage and train our mind, by training & Channelizing it we can Master of our mind.

In yoga sutra 1.12 Maharishi Patanjali gives us the solution "Abhyasa Vairagyabhyam tannirodha. Through this Abhyasa (Deep practice) and Vairagya (detachment) we can begin to reduce our thought waves. 

Abhyasa(deep practice):

Regular practice of conditioning, asana, pranayama and pratyahara will make our body steady and this Physical efforts will make our mind steady. But how long to practice, So Maharishi Patanjali says in yoga sutra 1.14 " Satu dirghakala nairuntarya satkara sevito drdhabumih" which means practice with consistent efforts for long time, without Break with full devotion and dedication, until the practice becomes firmly grounded.

Vairagya (detachment): 

Here detachment doesn't means that we don't engage with the world but being with them, doing our duty not get entangled or overly attached. most of our our thoughts arises due to attachment to material things,  people around, even from our internal thoughts and feelings. So by practicing some yoga techniques for detachment will reduce our vritis some of these are:

1. Pratyahara and yoni mudra:

Our chitta gather variety of things from outside world through our Senses and our mind is busy receiving so practicing pratyahara and yoni mudra will withdraw  our senses inward.

2. Practicing nispandabhava:

Here we sit comfortably without any movement and observe and passively listen to the sounds without thinking. 

3. Pratipaksha Bhavna: 

Some times we Identity ourself with this thoughts, and negative thoughts bothers us, so practicing pratipaksha bhavna will help us to counter this negative thoughts and instead help cultivate positive thoughts.

4. Reflection and Anitya Bhavana:

In this technique by seeing  things as witness we don't get entangled with them but we watch Watch what's happening in our life in Chronological order as if we are watching a movie without analyzing and judging it. This technique cultivate mental detachment and train our mind to become observer of our own thinking. Again  by using Anitya bhavana we learn to discriminate between what is permanent and what is not? And understand that every thing is transitory, so why should we get attached if nothing is permanent and everything is changing. 

Next solution Maharishi Patanjali gives us in yoga sutra 1.23  "Iswarpranidhanatva"

Which means surrendering to the will of God. while Doing chitta vriti nirodhah we have to develop Certain kind of devotion and surrender which will guide us and sail us through this journey. When something is in not our control and we can't do anything the best solution is to leave it to God, by surrendering our thoughts and mind we become free of this chitta vritis.

Bhagvad geeta shloka 9.34 Say: "mann-mana bhav mad-bhakto madhyaji-mam namaskaru"

Here God says to us engage your mind always thinking of me, became my devotee and worship me and you will surely come to me. 

So all this practices and techniques purpose is to get " chitta vriti nirodhah ".