When you have an agent that you can go to the Performance Institute, go in, but you have to do it on game day, the same day you have a game, but do it before the game of course, do your practice, gain the points to go on your attributes, add them, then when you exit, and the autosave comes up, save your superstar season, then go back to the calendar (you have to go to the calendar first) then go back out to the map.
Go the the Performance Institute again and you'll beable to do the practices again that gain you points, do it again and the previous points you got will still be on your attributes and you'll be able to add the ones you gain from the pratice you just completed. You can do it over and over till your attributes are maxed out.