Don't know if this has been posted before. Nevertheless, it should help the newbies.
1. Pick any team in Training mode.
2. Play against a team in the league for which you want to unlock. 3rd kits.
3. Play Free Practice. 11 players against 1 (the keeper).
4. Score 1 goal.
5. Quit.
6. Repeat 1-5 against each team in the league.
With this method, it took me about 30 minutes to unlock the Premiership 3rd kits. The biggest wait is for the training games to load.
1. Pick any team in Training mode.
2. Play against a team in the league for which you want to unlock. 3rd kits.
3. Play Free Practice. 11 players against 1 (the keeper).
4. Score 1 goal.
5. Quit.
6. Repeat 1-5 against each team in the league.
With this method, it took me about 30 minutes to unlock the Premiership 3rd kits. The biggest wait is for the training games to load.