Maintain your discipline
Boxing is not only a sport, it is also science and art combined. As such, the disciples of this art are forced to maintain the disciple itself and their own conduct. Discipline covers regular training, exercise and of course self-control.
Develop your own technique
What is there to add when everything seems to have already been discovered? Not much but there is still. From time to time, boxers develop their own boxing techniques that are different from everyone else's. These are oftentimes products of their own inquisitive desire to discover something new from an old craft, a product of combining techniques from other styles of fighting or a remade and polished technique from an old great.
Invest on character
Lack of good character is among the most treacherous factors why some boxers just don’t become great themselves. It is much harder to be humble when you know that you can pick a fight any time you want, hit a guy straight in the face and come out without a scratch. But then again, that is not the essence of boxing.
It is not simply brawling, it is also a test of character. If you are patient enough, if you have consideration for the other fighters enough to make you respect them, if you can look another fighter in the eye and see that he is not just a living punching bag, you will definitely understand that it takes more than fists to be a boxer. It also requires a good character.
All boxing greats have a common denominator. It is their personal investments on this field.