Well, first of all I suggest you read the guide + FAQ in the Help forum (http://www.buzzerbeater.com/community/forum/read.aspx?thread=144856&m=1).
Second, I really like to train players and for now I have no desire of winning games/championships, so take my advices having this in mind ;) The best way to train is to start with three young players (18-19yo), which you can play during the three weekly games (2 league games + cup/scrimmage). I don't recommend to train C for both C and PF, since it slows significantly the training speed.