training stamina and free throws is pretty pointless unless your entire team sucks.
It is better to concentrate your training on your youngest players (they train a LOT faster).
To do this you play your 18/19 years olds in the positions you are training for at least 48 minutes each week. Training updates every CET friday morning (not after each game). So a tip is to check your weekly stats on thursday night and then adjust your training page according to who you want to train.
Example:
If you have 2 18 year olds average at jump shot and jump range, respectable at handling and passing and outside defence. Then put them as PG and SG in your team that is playing and then train them for one of the skills they are good at. i.e. You set it training as Jump Shot for Guards.
Hope this makes sense and helps you understand the tricks of the training system.