Powerstar Golf

Playing through Career will naturally get you this but if you would like to speed up the process save any of the + XP bonuses you may get from a pack and use them on the 18 Hole Tournament rounds during career. This will net you more xp since it is a % of the total xp you earn during a round.

I also recommend posting scores in the free play so that others can play against you. If they don't win then you will be rewarded 500 xp per round you win.