They often develop strong personalities and will attempt to assert themselves. More structure and discipline is required of the coach. Understanding each player's psychology and good communication skills are also important. Technique should be solid at this age, but it must still be practiced regularly. Now, coaches can stress tactics, including 11v11.
Fitness requires more attention as players have developed physically.
Strengthening programs may include ply metrics. All training under pressure of the opponent. 8v8 to teach tactical concepts, more 11v11 stressing multiple systems of play. Continue to practice technique, but most time will be spent on tactics. Fitness becomes more important, also.