This is a question that was asked in the satsang with Sri Sri in the Bangalore ashram. Enjoy!

Q: What are the three types of dhrutis that Lord Krishna mentions in the 18th chapter of Gita?

Sri Sri: Dhruti means that which upholds or sustains life. For many people, the mind goes hay wire, They cannot even sustain or tolerate a small insult. A little bit of imperfection they cannot tolerate. Sattvic dhruti is that which sustains the mind, life energy, and activities of the senses. That which helps you to be steadfast in your yoga. Not like one day you do yoga and next you go for bhoga. Not like that. That which upholds your senses, your life is sattvic dhruti. Rajasic dhruti is of the type when I get results then I will deliver. This sort of mindset where your enthusiasm is related to some little reward is rajasic dhruti. It could be related to Dharma or it may not be related. Any work that is taken with the intention of getting results, such as fasting to achieve some results. What is God going to get is you fast? 
Tamasic dhruti is one who sleeps a lot. That is most important for them. Nothing else. Very fearful. You look at their face, they are always down, depressed.
If you cannot get married, you are upset. You get married, you are upset. This is tamasic dhruti. Always regretful. That should not have happened. I should have had like that. After 40 years of marriage, they think they should have married someone else. And arrogance. And one is unable to get of this negativity in the mind. Some people try to get out of it, but they are not able to get out of it. Lazy people, who can sleep anywhere, any time. In Kerela, I heard about a person that he can sleep at the dining table while he eats. Once I stayed at such a person’s home. That person’s servant, told me that my Master falls asleep while talking! Doctor said lets do a scan. A few years ago, the CT Scan was a new machine. He went for the scan. The doctors were wondering why is the machine making so much noise. He slept in the scanning machine and was snoring!
This happens when you do not have any aim in life. Often Ashrams are the base for lazy people. But we do not have this issue. In Ashrams, there is a issue about how to keep people busy. If you keep doing some activity, then you will not get lazy. 
One who is lazy, gets scared easily. Then behind fear, comes negative thoughts such as who will cremate me when I die, who will take care of me when I grow old. Some one will complete the cremation rights. Man is mad. If you do not want to leave the madness, then be mad for that which has made all these things not for the things made by Him. Then after this comes vishaad: they think about what happened many years ago and get upset. People will reach Mumbai from Bangalore, and then they will continue to say we should have booked another ticket. Vishaad has become a habit. A person who is enthusiastic and happy, they will not go into vishaad.

Then comes ego. People are in vishaad, often walk with arrogance. Have you seen the people who lost the elections? A wrestler falls and then he says there is no mud on my mustache, where have I fallen? One who cannot come out from a negative mindset. 
Now we have to see what type of dhruti we have: sattvic, rajasic, tamasic.

How to get out of this? 
Do seva, sadhana, satsang. 
Tamas gets converted to Rajasic and then to Sattva. 
If you are surrounded by Tamasic people then you will have more of that type of dhruti. Often kids say, throughout my life, no one has done anything for me. The way you behave in front of kids affects kids also. If you are in Tamo guna or rajas guna, then kids catch on to it very fast. Similarly, when four people get together, and one person says something negative and everyone else contributes negativity, then after half an hour when people go home they are so tired.

How to transform from Tamasic dhruti?

This path: Seva, Sadhana, satsang, right company.
Like dhrutis, doers are also of three types. Sattvic doer is happy whether work happens or not. 
Rajasic doer is happy if work gets done and unhappy when the work does not get done.
Tamasic doer is one who does not know what they have to do. And they are in vishaad.