How to develop non-attachment?

Thought patterns are either Klishta or Aklishta.

• Klishta means that they are not neutral, but are colored or afflicted in some way, such as with attraction or aversion. These lead to pain and suffering.
• Aklishta means they are not colored, such as when not afflicted either with attraction or aversion. These do not lead to pain and suffering.

Knowing if a thought is colored or not-colored  brings freedom of choice to act or not act.

See also the article on Klisha and Aklishta Vrittis, as well as Yoga Sutras, particularly sutras 1.5-1.11 and 2.1-2.9.

A most important practice: To observe whether thoughts are Klishta or Aklishtais extremely useful. It is the foundation practice of observing your thought process. This is done when observing both individual thoughts and trains of thoughts. This can seem so simple a practice as to brush over it as being unimportant, but this is a big mistake. Observing whether thoughts are coloredor not colored is useful both at meditation time, and during the activities of daily life.

Klishta, or colored thought patterns:

• Often these have a disturbing quality.
• Sometimes they are just distracting, not really disturbing.
• At other times we may enjoy or cultivate the thought patterns, although they are still colored. In other words, we like our attractions. 
• Interestingly, we also hold on to our aversions in such a way, that it is like we want to keep them around too.
• Many of the mental impressions that seem to be related to "I" or "Me" arecolored, or Klishta.

Aklishta, or not-colored thought patterns:

• These are neutral. Much of the information stored in our mind is merely data that is there for day-to-day living. Household or office objects are good examples of objects whose impressions are naturally neutral.
• In a public area we see many people, some of whom we may have seen before, but do not know. These too are often Aklishta, or uncoloredmemories.
• Sometimes we have thought patterns that were previously colored, but have lost some, most, or all of their coloring. Good examples are past habit patterns that we have truly let go of. The thought impressions of those past habits are now mostly neutral if the habit has really been changed.
• Are useful on the spiritual journey

What to do: 

Observe the rise and fall of thoughts: Simply observe the individual thought patterns that naturally flow in the stream of the mind. They rise and fall as a normal process. Then, simply observe whether a certain thought pattern isColored or Not-Colored, Klishta or Aklishta.

Literally ask yourself: "Is this thought colored or not colored?" "Is this thought klishta or aklishta?"

Talk with yourself: The way to observe is to literally ask yourself with your inner voice, "Is this thought colored or not colored, klishta or aklishta?" Answers will come from within.

Literally answer yourself: "Colored" or "Not colored" "Klishta" or "Aklishta"

Verbalize the words: You will then want to train your mind by internally saying the word or label, such as "Colored," "Not-Colored," "Klishta" or "Aklishta". (This goes along with the process of observing whether the thought is Useful or Not Useful, which is described in a section below.)

The process might go something like this:

1. Thought arises.
2. Ask, "Is this thought colored or not colored?"
3. Answer comes, "Colored!"
4. Ask, "Is this thought useful or not useful?"
5. Answer comes, "Not Useful!".
6. Train the mind with, "Mind, this thought is not useful!"
7. Then you can either let go, explore, or cultivate the thought. (The effect of this is cumulative. It may seem slow at first, but it builds up over time.)

With a little practice, the process comes very quickly, something like this:

1. Thought arises.
2. "...Colored... Not Useful..."
3. "Let go of it, mind...." (or explore it further if you choose)

Or:

1. Thought arises.
2. "...Colored... Useful..."
3. "This is a good idea... I should do this..."

Or:

1. Thought arises.
2. "...Not Colored..." (or only mildly colored)
3. Thought naturally drifts away.

Intentionally allow a thought to arise: Practice this by intentionally allowing a thought pattern to arise from within, and then observe and label it. Do this practice several times allowing different types of thought patterns to arise. With practice, this will be a very easy thing to do. Then, as a natural outcome of theobserving and labeling process, it becomes much easier to become a neutralwitness to that stream of thought patterns.

Examine individual thoughts: When we can neutrally witness the entire stream of thoughts, it is then easier to examine individual thought patterns, so as to further weaken their grip (weakening the samskaras that drive karma). It is also easier to begin to move beyond the mind itself, towards the center of consciousness.

Allow colored to become uncolored: We come to see that a most important aspect of yoga meditation has to do with allowing Colored or Klishta thoughts to naturally transition into Uncolored or Aklishta thoughts. The original thought remains, but gradually loses its coloring (mostly attraction and aversion), resulting in those previously troublesome thoughts becoming mere memories. This is a practical method of attaining the true meaning of non-attachment (vairagya).

Source: http://www.swamij.com/witnessing.htm