Know the Field
In the Arena, you’ll have two watchtowers and a castle on both sides. A moat separates the two lands and there are two bridges (on the left and right) for units to use to cross over. Keep in mind when you’re placing your cards that wherever you drop a unit, that is where they’ll land. So, let’s say you have a Goblin Hut out on the field. Drop someone behind it and they’ll have to go around the hut, costing some time. On the flip side, if there’s an enemy unit charging up (like the Prince), drop a random small unit in front of them to hinder their advance. Also, keep in mind that when you take over a watchtower, that plot of squares becomes yours allowing you to place units there as you please. This is good to get even more units closer to the enemy castle, adding insult to injury.
There’s a plethora of strategies you can adopt in your quest to be the best ruler in Clash Royale.