Boost can your player through training. Your players will earn experience points but that experience will not be added automatically to their final level. The only way for them to increase their level is by training. To do this, go to the "Player Badges" menu then select the "Train" option. Once there, you can use different player badges to train the player you wish to level up. Have at least ten cards to spend before doing this or the costs will be too prohibitive. Training a player with a full ten card set will give you the maximum experience. The rarer the cards used for training, the more experience points you will get. When selecting a player to train, start with your best player. Those with a three star tier will give you more potential for your team in the long run. Start boosting them during the early phases of the game. You should also train players who can handle different positions in game so you can use their cards to the fullest. Split your training to five players. With this training arrangement, you can train two offensive players, two midfield players and one defensive player. Maximize this by start training offensive players and midfield players, as a strong offense helps your defense.