Improve your team by improving the Coach
No matter which team you chose to play with, your coach will be one of the most important assets after the players. You can head on to the My Team tab and then tap on the team's coach icon. There you will be able to pay some GP from the Set Strategy tab and select from various game strategies. You can try them all out in normal matches, to see which one works the best with your current players, and when you finally acquire all the players (assuming all star players) that you want to your team, then you can start polishing the strategy which your team will stick with.