Try to replace all your Common cards with Uncommon or better as soon as possible. The better stats will help a lot. Sometimes the boost you get from using compatible cards in a tag team match will be more beneficial than simply choosing a card with higher stats, so choose wisely. Just keep playing. Even if you lose you'll still be able to draw a card after an Exhibition match. And even if it's a card you don't want you can still use it to improve your favorites.