You can increase your Overall, Awareness, and Stamina in Practice mode by having your superstar get practice points by getting a big gain on offense or creating a big loss on defense. You also can get your stats up by getting an agent that has access to the Performance Institute and get a medal on it:

Bronze: 3 points
Silver: 4 points
Gold: 5 points

Note: Your stats are not permanent. They will be reset after each game. You must do the practices and Performance Institute again to get them back up.