Those who live according to the flesh have their minds set on what the flesh desires; but those who live in accordance with the Spirit have their minds set on what the Spirit desires.The mind governed by the flesh is death, but the mind governed by the Spirit is life and peace.
"Self" is one's own nature, character, abilities, personality etc. It is part of one's mental or physical nature.
"Discipline" is the training that produces obedience, self control, or a particular skill. Control is gained as a result of this training.
We should know that as Christians, our self, the flesh will always want to show itself at anywhere anytime.
And it is of great necessity to control our self and all fleshy desires because the end of it is not always a good thing.
Temptations, trials and tests will always come, it is important that we try as much as possible to Discard flesh and self if we want to run this race to the end.
There are three (3) ways one can actually discipline "Self".
The lust of the flesh: The lust of the flesh is the preoccupation with gratifying physical desires.
The lust of the eyes: The lust of the eyes are materialism craving and accumulating things for oneself wanting to have all what your eyes see and admire.
The pride of life: The pride of life is the obsession with one's status or importance.
Brethren, all these things will always come, so please, learn to discipline Self and its desires.