Story related and cannot be missed.
This is the first cup you'll win in the story. There's no real way to speed up achieving this, as you'll need to follow the story quests to initiate the Soccertown Cup competition.
The only real 'tip' to offer would be setting the match difficulty to 'easy' in the options menu, as this really does make the three 4 minute matches you have to play (the friendly match to unlock the Soccertown Cup, the semi-final match, and final match) very easy to win and save any messing around with having to replay the matches if you draw or lose.