Well, my tip (adding to the above) is to ignore coaches and scouts to a certain degree, at least about stars (although scouts are VERY useful by telling you tips on adaptation, injury proneness, consistency and big matches). You will get fooled a lot of times:
1) I bought James Rodriguez with 3 stars potentital. 1 week after, he had 3 and a half (and is a **** good player).
2) I bought Thiago from Barcelona with 2,5. One week after he had 3,5.
3) Willshere broke his leg a second time in my Arsenal save. His potential went to 2 and a half. After one season of playing, he's back in 3 and a half.
4) Meanwhile, Chamberlain had 4 stars of potential, and he's far worse than Rodriguez or Wilshere.
5) Stars are based on team average so, if your team is getting better, stars will be getting worse.
6) A lot of youngsters get 4 stars potential and they'll never be that good (for example, players with very low physical or mental attributes).