The championship has no financial stake. Do not sacrifice training to win matches unless your goal is really to slam your friends.
Play the more friendlies you can. They will provide additional training far from negligible. Think a friendly is about equal to a league match.
Test your youth with uncertain scouts comments to try to discover their talents. Try to lose the least possible training on your strong players already in place.
For that : use replacements as needed. If a position is occupied and you have a rookie potentially very interesting to test here, make him play here the last 5 minutes instead of the worst of your players.
You are not obliged to know well all your players at your fingertips and spend a lot of time. Often, one or two tests are sufficient to determine the approximate quality of a youth who could potentially be of interest for your current training. Then you'll watch the evolution of trained players especially promising. Follow the others is optional and not to do so does not really cost you much in the long run.
You can adjust the time you spend managing your youth team by focusing on your best young. This has the advantage of dispersing yourself less and ensuring efficiency in the management of young people who deserve it.
Generally try to maximize the level of your players in at least two skills which are well combined before they are promoted. Try to leave the relatively young mature before thinking about the age of exit. Promoting a young "passable" scoring "weak" passing 17 years and 3 days doesn't worth a "solid" scoring and "inadequate" passing one of 17 years and 50 days when he has the potential to reach it. Think about it, and do not ruin your efforts in the money time.