This will be a bit of a grind for those who don't enjoy the My Player mode. Complete all drills, Do well in each game, Save milestones for Key Games if possible. Maxing out Offensive awareness and Defensive awareness will increase your rating quicker. After those are maxed out continue to max out stats that play to your position.
Thankfully In 2k12 you start My Player at a 60-63 overall. At 15 games into my season i was already a 67 (without putting anything to awareness) Look for this to take anywhere from 40-70 games (depending on what you spend your points on).