Each fighter comes with five ability cards, and they cannot be switched out or traded between fighters. Take a look at those too before you swap out a fighter, because you don’t want to accidentally give up your favorite abilities. Sometimes these can make the difference in a close call between two equally-strong fighters.
You don’t have to use cards of all different colors to make your teams, even though it’s often generally recommended. Another suggestion for “one style” fighters is to go with nothing but red cards. If you’re a brawler, this is the best solution because red has the highest drag attack and the highest instance of attacking cards. Maybe put a yellow and/or a black in there too, for healing and/or buff cards and nerf cards.
You’ll earn rare cards, as mentioned before, from the Dragon Stone eggs, but often you’ll end up running out of card cost space in your deck in which to put all of your rare fighters so you’ll have to put common ones in to lower the card cost. This is where the regular (Dragon Fang) eggs come in handy, because they are an excellent source of two-star cards. You can either load up your deck with two-star cards, or put something like one four-star and four one-stars in. Generally, only put the 4-star in with 1-stars if it is a red one, as the drag attack will be sky high.
Coins are not as necessary as the other currencies, but if you want to do evolutions and combinations in the lab, they are absolutely necessary. Aside from fighting card battles, you can also earn coins by completing the daily and global quests. Once you unlock PvP mode, you’ll be able to earn big coin bonuses depending on what rank you reach.
Often you’ll earn cards that are meant for use strictly as material cards when combining. They will be as good as useless in battle, but when you use them as a sacrifice, they will give massive amounts of experience. Save these for your rarest cards. Also, save it for a card of the same color. The same color card gives you a x1.5 experience multiplier for free, which, of course, is huge when you’re talking about a strictly material card.
Any time that you need to earn more experience points or coins, or cards, go back to any older stages that you have already beaten, and play them again. You will earn the same amount of coins and experience as last time. Do this for as long as you need to until you have enough cards and coins for combining/evolving, or until you unlock whatever it is that you want to unlock.