Learn when countries produce their newgens and scout them right when they are generated. You'll have to do this manually team by team. Then buy them up and have a blast.
By searching for value and have the age set 21 or younger (or whatever age). Look for the highest price or then search for certain criteria like finishing for strikers, etc.
It varies country by country, as can be seen in Chris's link above.
As for finding them, having good Scouts can help, but I always go for the manual option, just searching through U21/U19 International teams, or "Choices" method 2 posts up