Early army, or late-game warfare?
You should probably already know that purchasing multiple of the same kind of unit will allow them to fuse, creating even stronger units - just as in every other auto-battler, this is important here.
But the question is, do you want to splash hard cash on some relatively low-powered units and struggle your way to the top, or do you want to save your money for when the rarer and more powerful units are available in the shop?
You will definitely need some units on the field to get started with everything, naturally, but saving some extra cash for when things get serious isn't a bad idea at all.
Strength in numbers and synergies
Now you've decided on whether to save money or get a big army, it's time to think about what kind of army you're going to build. And hopefully it's a big one.
You can spend coins on expanding the number of units you can put on the field, and this will give you a massive advantage in the early game, and that advantage only gets bigger as the game continues.
But also you need to keep an eye on synergies. You should attempt to combine multiple of the same kinds of class and faction monsters, and they will buff one another. Multiple plant-type monsters, for example, will offer a healing effect to the rest of your team.
I have the high ground
There isn't actually any high ground in Auto Brawl Chess, of course that's just a poor Star Wars reference, but positioning is very important, as in any war of attrition.
You definitely want your strongest warriors, with the highest HP and defence, up close to your opponents, but somewhat spaced out from one another so they don't get devastated by AoE attacks.
Likewise, you want your long-range fighters to be positioned behind them, so they can get protected by the frontlines, while also doing massive damage. Just watch for special units who will be able to get behind your team…
Eye on overwatch
This is an auto-battler of course, so what you do during the battles doesn't matter too much, but it's important that you watch closely, especially when you are whittled down to the final few opponents and can see what strategies they use to get ahead.
You will need to pick characters and devise counter-strategies quickly in order to stay ahead, and figure out how to take down the strongest and most powerful of enemy players with your team.
In addition to that, you will need to manage your gold and the team you've got sat on the bench in waiting. If it's getting to the final few rounds, go all out on spending gold and making your team as big and powerful as possible.