Bhagavad Gita Verse 23, Chapter 18

niyatam sangarahitamaraagadveshataha kritam |
aphalaprepsunaa karma yattatsaattvikamuchyate || 23 ||
 
That action prescribed by scripture which is performed without attachment, without like or dislike, by one without hankering for reward, that is said to be saattvic.
 
niyatam : prescribed by scripture
sangarahitam : without attachment
araagadveshataha : without like or dislike
kritam : performed
aphalaprepsunaa : one without hankering for reward
karma : action
yat : that which
tat : that
saattvikam : saattvic
uchyate : is said
 
We came across three types of knowledge or world-view in the prior three shlokas. Now we come to the topic of the karma, the action itself. Knowledge is the main instigator of any action. So if the knowledge is saattvic, the action will be saattvic and so on. A simple way to differentiate between the three types of knowledge is the gauge the severity of the likes and dislikes, the raaga and dvesha, that the knowledge creates. When we only see unity and harmony, without any likes or dislikes, that is saattvic knowledge. When we have strong likes or dislikes for this object or that person or that situation, it is raajasic knowledge. When we have a extreme or perverted like or dislike, it is taamasic knowledge.
 
Imagine that you are a guest at a friend’s house. A group of young children are playing a game of monopoly that they ask you to join. Some children want you to win, since you are in their team. The other team wants you to lose. At the conclusion of the game, you end up losing all your monopoly money. But you do not harbour any feelings of resentment or anger towards the children. Why does this happen? You have no attachment to the monopoly game, the money or property that you have acquired, since you know that it is not real.
 
Shri Krishna says that any action performed without attachment, without like or dislike towards any part or character in the action, without hankering for the reward of the action, such an action is a sattvic action. In other words, while commencing the action, our intent and our state of mind is saattvic. We will only be able to perform such an action if we have reduced our likes and dislikes towards material objects to a great extent. This happens only if we see the world as illusory and ephemeral, either through seeing everything as Ishvara’s Prakriti or through meditation upon the hollowness of Maaya.

Bhagavad Gita Verse 9, Chapter 18

kaaryamityeva yatkarma niyatam kriyaterjuna |
sangam tyaktvaa phalam chaiva sa tyaagaha saattviko mataha || 9 ||
 
Whatever action is done, should be performed only as an obligatory duty. In this manner, giving up attachment and also the reward, that giving up is saattvic, in my opinion.
 
kaaryam : action
iti : in this manner
eva : only
yat : whatever
karma : actions
niyatam : obligatory
kriyate : is performed
arjuna : O Arjuna
sangam : attachment
tyaktvaa : giving up
phalam : reward
cha : and
eva : also
saha : that
tyaagaha : giving up
saattvikaha : saattvic
mataha : opinion
 
Shri Krishna explains the correct way, the saattvic method, of performing actions. Let us look at this step by step. The first step is to only perform actions that are within the realm of our state in life, our aashrama, and our career, our varna. Actions that are prohibited or actions that are purely out of selfishness should not be performed. These actions are termed as niyatam karma in the shloka. A high degree of awareness is required to first ensure that we are not stepping into any prohibited actions.
 
The second step is to give up attachment to the reward, the phala, the fruit, of the action. Attachment to the reward need not be something tangible and physical. It could be subtle things like praise and adoration received from others on successful completion of the action. It could be a subtle thought such as "I have helped that person, so nice of me to do so". The goal is to slowly wean the mind away from its natural tendency to expect rewards for every action. We can do so my substituting our personal motive with a motive for selfless service.
 
The third step is to give up attachment to the action itself. We saw the types of attachment to action in the previous shloka, including attachment to the completion of action and attachment to one particular way of performing the action. The key is to realize that at every moment, we are giving it the best of our ability and attention. The rest is upto Ishvara, since there are several other factors at play in the outcome of an action. But in no circumstance should our energy level go down. We have to combine energy in our work with indifference to the reward of the work.

Bhagavad Gita Verse 8, Chapter 3

niyatam kuru karma tvam karma jyaayo hyakarmanaha |
shareerayaatraapi cha te na prasiddhyedakarmanaha || 8 ||
 
You should perform prescribed actions, since action is superior to inaction. Also, even the journey of the body cannot be accomplished through inaction.
 
niyatam : prescribed
kuru : perform
karma : actions
tvam : you
karma : action
jyaayah : superior
hi : since
akarmanaha : inaction
shareera-yaatraa : journey of the body
api : even
cha : also
te : your
na prasiddhyet :  not accomplished by
akarmanaha : inaction
 
Having covered the topic of why one should perform action, Shri Krishna now speaks about what kind of action should be performed. He urges Arjuna to only perform "niyatam" or prescribed actions. What does this term mean?
 
Scriptures classify actions into several categories. Let us look at the two main ones: "niyatam" or prescribed actions, and "nishiddha" or forbidden actions . Prescribed actions are those that are enjoined in the Vedas. But in today's context, we can interpret this as one's duties. These include performing one's svadharma, serving one's parents, family, and nation etc. Forbidden actions are the "thou shalt not" actions such as killing another being, stealing, cheating and so on. So here, Shri Krishna urges Arjuna to perform prescribed actions, but without any trace of attachment to the action or to the fruit.
 
Now one may say "I like to watch a movie and enjoy a good meal. Those do not seem like prescribed duties. How should we think about those?". Shri Krishna does not advocate repressing anything, as we saw earlier. But we should to define boundaries to any action, as well as minimize attachment or selfish motive. The best way to do so is to share.
 
If you want to watch TV, watch it collectively with your family and friends. Or share your meal with them. Doing so will ensure that our previously self-serving actions lose any trace of selfishness or ego. The best example here is a mom that always cooks what the family members like, and puts her preferences on a lower priority.
 
In addition, Shri Krishna reiterates the notion that one should never resort to inaction, He says that if one does not act, one cannot even perform maintenance of one's body.
 
Our body is an important tool in our spiritual journey. Nowhere in the Gita has Shri Krishna asked us to neglect it. In fact, here he is saying that one should absolutely perform action to maintain the body, including bathing it, feeding it, keeping it strong and fit, and going to the doctor if it is not working properly. It is an extremely practical teaching.