Bhagavad Gita Verse 7, Chapter 3

yastvindriyaani manasaa niyamyaarabhaterjuna |
karmendriyaih karmayogamasaktah sa vishishyate || 7 ||
 
But one who controls his senses by his mind, O Arjuna, and performs karmayoga with his organs-of-action without attachment - that individual is superior.
 
yah : that
tu : but
indriyaani : senses
manasaa : by mind
niyamya : controls
aarabhate : follows
arjuna : O Arjuna
karmendriyaih : through organs-of-action
karmayogam : karma yoga
asaktah : without attachment
sa : that individual
vishishyate : is superior
 
In the previous shloka, we saw that repressing our urges and giving up actions does not work. A different approach is needed to clean our vasanaas and selfish desires. In this shloka, Shri Krishna says that we should not give up actions - instead, we should give up attachment.
 
Giving up attachment is a technique unto itself, and this chapter goes into a lot of detail on that topic. To begin with, this shloka informs us that we need to arm ourselves with two weapons: discrimination or "viveka", and dispassion or "vairagya".
 
Let first look at discrimination. If we have followed the teaching so far, we know that material objects are are temporary and are not the true sources of happiness. But it is extremely easy to forget this teaching, especially if we have strong vasanaas and desires.
 
Therefore, we have to constantly arm ourselves with the weapon of discrimination by being always aware and alert about our thoughts and emotions. And we have to be especially alert when we are around objects that we are attached to. For a simple example take food: it could be chocolates for the sweet tooth person, fried food for the obese person etc.
 
Next comes dispassion. If we constantly practice discrimination, dispassion will happen automatically. Objects, people and situations will begin to lose their hold on us. Dispassion will prevent our energy from rushing out into the world of material objects through our senses. This is what the shloka means by the phrase "one who controls his senses by his mind."
 
Finally, once the mind has gained back control over the senses, then the energy that once rushed out through our senses can be channeled into performing karmayoga. The next shloka will go deeper into what Shri Krishna means by karmayoga.
 
Footnotes
1. Verse 375 of Shankarachaarya's Vivekachoodamani speaks of dispassion and discrimination as "two wings of a bird" that lift the seeker into realization.