you can only train one discipline per week (48 mins of game time will give them full training for the week, check your weekly stats to see how many minutes your guys play in your training positions). Its up to you and based on your roster what you should train. Identify who are your best young stars and focus on them. Minimum rating for the guys you should focus on are "stars" and above. There is little or no use in training guys who are over 24 and who have very little chance of growth due to their potential ratings. Hope that helps.