Create a player in Homecourt mode, then save and exit. Go to the main menu and select "Play Now". Your player will appear on any team you choose, as long as your profile with that player is loaded. Choose any team and select your player and two other players. The other team can be any desired. Then, play the game out to 100 with no GameBreakers, focusing on the skill you wish to increase. At the end, win or lose, your player will still have an increase in attributes. Do this a couple times to maximize all stats, then go back into Homecourt mode. Play through until your baller levels up a few times then repeat. Once Homecourt mode is complete and your baller is at level 20, go back into "Play Now" mode and completely maximize all his stats.
When you unlock the GameBreaker within a match, pass the ball to your player that is the best at performing tricks and skills. Wait near the halfway line until an opposing player tries to steal the ball from you, then press TRIANGLE to "skill" them. This gets your multiplier up. Repeat this two more times to the same player in quick succession to set the multiplier to x4. When this has been achieved, either immediately do lots of crossovers to fill the meter at the top or hold SQUARE to perform a more complex skill. When the meter is filled, do a double dunk or long shot with a player. Instead of getting 2 points you will earn 5 points.