In order to easily win your matches, simply score more points than your opponent (even if it is just more 1 point than them), get the ball with one of your characters and move him to the lower left side of the field. Then, release the controls of the console and just let your character in there.
While the time elapses, the opponent near you can't take the ball away, due to a glitch, and therefore you'll win the match.
In order to unlock a certain number of teams, input the stated passwords in the Password option from the main menu.
In order to unlock new players, you have to score a total score of the stated points in your matches.