Improve your cards every chance you get. If you've got a strong deck built, your first order of business is to make sure you upgrade them as much as possible. Find the strongest card you've got in your collection and level it up as much as you can. Continue this with every card you own, starting at the strongest and ending up with your weakest. If you keep at it, eventually you'll have a set of cards that you can just keep reusing and rotating out without having to rely on the same ones over and over.
Don't shy away from racking up premium currency. This kind of currency makes the world go 'round, at least in the world of freemium games, so don't be afraid to "sell out" and watch the ads you can view here and there to earn 3 gold coins apiece. You can spend them in turn to get new cards, which you can always use, and to use Power Plays, which can be infinitely useful.
Learn to use Power Plays and benefit from them. Power Plays are huge when it comes to gaining the upper hand in several matches, and while they require a little more input from you than you may be willing to give, they're awesome at putting you in the lead. You can pass the ball by swiping the screen, or a series of what can pass as other "quick time events" during matches to earn an additional card or even win the battle you're in. They will take some practice to conquer, but it's absolutely worth doing so.
Choose your friends and choose your enemies. When you're faced with player clashes, choose the card that will fell your opponent, just in case you lose the player clash. Don't use your best cards and stay safe -- this way you don't have to take as many risks. And when you're completing tournaments, you can choose which rival you're going to play with. Because you can see who they're using, be choosy. If you see one with cards that will decimate yours, choose another rival. No difficulty in doing this, and you can't lose.
Evolve a card to your best ability. Card evolution is absolutely essential to playing well, especially if you want to get as much as you can out of even the weaker ones. Level up your card to its max. You'll then have to gather up 100,000 silver as well as an Evo card. When all of these pieces are in place, an Evolution can begin. Make sure you do them as often as you can, but make sure you're doing them at the right time as well -- namely, when you meet all the requirements.
