Play Challenge Matches until you have a good line up. Once you find a potential card that can be used for the long run, improve its levels to get its full potential. Play Skill Matches when you are ready then do Friendly Matches where you have a chance to earn extra Friend Points for cards. To get the top tier players, you need to open a Premium Box, which is purchased with Energy Balls (premium currency). You can get free Energy Balls by completing the Academy quests and challenge matches.