Guide is right here on the forum:
(144856.1)Local managers are usually very eager to help you get started. If you like training, try contacting the U21 coach, they're usually looking for managers to train young players to help the U21 team. You don't need expensive high potential players for the U21, after the draft you can probably buy a player with 50+ total skill points (TSP) and perennial allstar or superstar potential for below 50k purchase.
However, financially it might not be the best to invest in training early in your career, as it doesn't pay off anytime soon. The best thing to do financially is to invest in your arena, and then some cheap veterans that help you win games to fill your arena.
That being said, this is a game that should be fun, and if you think training is fun you should go for it.