Bhagavad Gita Verse 19, Chapter 3

tasmaadasaktah satatam kaaryam karma samaachara |
asakto hyaacharan karma paramaapnoti purushaha || 19 ||
 
Therefore, always perform prescribed actions diligently without attachment; for, by performing action without attachment, an individual attains the supreme.
 
tasmaat : therefore
asaktah : without attachment
satatam : always
kaaryam : prescribed
karma : actions
samaachara : diligently
asaktah : without attachment
hi : because
aacharan : perform
karma : action
param : highest
aapnoti : attain
purushaha : an individual
 
In this shloka, Shri Krishna concludes his answer to Arjuna's question from the first verse in this chapter. Arjuna had asked Shri Krishna as to why he should commit the act of war, which in his opinion was a ghastly act. Let us recap Shri Krishna's answer.
 
Shri Krishna replied by explaining that no one can flee from action, that one should perform selfless rather than selfish actions, that selfless actions in the service of a higher ideal do not create bondage, and that performance of selfless action or yajna is the key to participating in the evolution of oneself and of the universe.
 
Another point emphasized in this shloka is that karmayoga should not be something that is restricted to only a few aspects of life. The karmayoga mindset should eventually become second nature, in other words, it should be embedded in each and every action that we perform. So therefore, in each and every action that we perform, from writing an email to eating our meals, we should remember to derive joy from the action itself rather than in the result. Only then will we begin to drop attachment to the action and to the result.

Bhagavad Gita Verse 9, Chapter 3

yajnyaarthaarkarmanonyatra lokoyam karmabandhanaha |
tadartham karma kaunteya muktasangah samaachara || 9 ||
 
Other than those actions performed for yajna, this world gets bound by action. Therefore, O Kaunteya, perform actions in that regard, without attachment.
 
yajnyaarthaat : done for yajna
karmanah : actions
anyatra : except
lokah : world
ayam : this
karmabandhanaha: gets bound by action
tadartham : for that purpose
karma : actions
kaunteya : O Kaunteya
muktasangah : without attachment
samaachara : observing
 
So far, Shri Krishna spoke about why performing action is essential, as well as what kind of action to perform. With this shloka, he begins the main topic of this chapter, which deals with how to perform actions. The second chapter mentioned it briefly, but this chapter goes deeper into it.
 
Shri Krishna uses the beautiful metaphor of a "yajna" to convey this teaching. In Indian culture, a yajna is a formal ritual of worship. Firstly, we fix a higher ideal before commencing a yajna, and dedicate the entire yajna to that ideal. Typically, that ideal is a "devataa" or a deity. Secondly, we perform actions such as chanting mantras and pouring oblations into the sacrificial fire, but do so with absolutely no trace of selfishness. Some mantras even include the words "naa mama" or "not me" to make unselfishness explicit.
 
So how does that ancient ritual apply to us? Let's look at a practical example. An accountant working for a corporation can be successful if she acts in the spirit of a yajna. She should set a higher ideal, e.g. "I dedicate myself to the success of this corporation". Then, she should perform her job responsibilities in the service of that goal. She will, for instance, frequently sign large cheques where there are opportunities to play games for selfish profit. But she will not even think about such things because her focus is on the company's well being, not hers.
 
Now let's see what happens when her goal becomes becomes selfish. She will begin to do things that generate "conflict of interest" in corporate-speak. She may slowly divert some of the company money to a shell company owned by a friend and so on. From a wordly perspective, she will get kicked out of the company sooner or later. From a spiritual perspective, each selfish action will bind her, propelling her into further selfish desires, and away from self-realization.