You should take a look at the scout report, which will show the strengths and weaknesses of each player, like jere92 said. It's good guidance.
Also, players might develop well or disappoint you in areas not covered by the scout report. All attributes not listed as strengths or weaknesses there could max early or strike a chord. It depends and you might have to gamble.
If you want to briefly understand what the stars mean (in terms of numbers), this thread from the brazilian forum might be of your interest:
https://www.managerzone.com/?p=forum&sub=topic&topic_id=12638592&forum_id=47&sport=soccer