The defensive player
One way to play the game that could be a safe one for new players is to be more defensive. So, what this means is; instead of placing your cards as close to the enemy towers as possible, you take steps back. Place your cards near your towers to help defend them.
Characters will automatically move towards enemy territory so your defense may not last long, especially with enemy cards coming your way. So, one thing that is a good idea is to place the cards you want behind your towers. This is a strategy that the game itself will mention, and it's a solid one.
So while your characters slowly move away from behind your towers, there will be time to defend them as they charge forward. While doing so, you can sneak in a card that you could place closer to the enemy zone. So although overall, this is a defensive move, you can sprinkle in a bit of offense too.
Ah, yes, speaking of offense, right? Well, if you love going in and dealing damage, then this is the playstyle for you. This strategy is essentially the opposite of what the defensive style is. So this means that you'll place your cards as close to the bridge as possible.
This will put you in attack mode so go ahead and unleash on those castles. Just know that they will be ready to defend. Also, like with the defensive strategy, it would be wise to keep a card in the back to defend, even it's just a little bit.
Your castles will fire cannons automatically, but the extra protection is always nice. But, if you want to be aggressive, then this is your chance to do so. If you're lucky, then maybe you'll take out the castles in no time. Who knows, maybe you'll whittle away at the health of the big tower and win your match early. Just play your cards right (quite literally) and you'll have a shot.
The projectile player
So in Clash Royale, some of the cards you can collect are projectile types. These can be arrows, fireballs, and other deadly launchable things. You can fire these right at the castles. They don't do incredible damage but do enough to keep them on their toes.
Now, you won't be able to use these cards every single time since because they rotate after each use of a card. So, a good way to approach this playstyle is by placing a couple of cards near your towers to help keep it defended while you wait for the projectile cards to be available.
You can choose to go all offense if you wish by placing your hero cards near enemy lines, but if your goal is to use your projectiles, then it may be smart to use your other cards on defense. This way, you'll get a nice balance to both tactics. Deal some damage while helping to keep your towers safe. This strategy isn't for everyone, but feel free to give it a shot and see if it's up your alley.