In order to unlock the AFC/NFC Hall of Fame teams (like the Glaciers, Dummies, et cetera), you must complete the in-game Fantasy Challenge. To unlock these teams so you can play as them, you must beat them in Supreme League mode; otherwise, you will only get to play them, not as them.

To increase your chosen characters statistics faster, hence making him a superstar more rapidly, try the following exploit. On gameday (Sunday), enter the Performance Institute and complete the exercise. After exiting, head over to your teams schedule and enter. Then, exit back out to the city map, and the Performance Institute exercise will appear again for you to use. You can do this over and over again if you want.