Early on in the game, you don't need to worry about separating your troops and using all of their individual abilities. Since the beginning is all about survival, just group them all together and use them for defense or taking out some smaller armies.

Once you gain a larger army, be creative about how you attack the enemy. Try using the so-called pincer movement when you attack from both sides with various troops depending on their weak spots.

Use a single unit to do some basic explorations early on. You need to learn as much as possible about your surroundings, so that you would know where to place the defenses.

Use the first attacks on your base as indicators of where you need to improve your defenses.

When you're attacking an enemy base, don't just focus on damaging big structures at all costs. As you do that, the enemy infantry will destroy your units before you even realize it.

If a certain type of units keep getting slaughtered in the battlefield, it might be that they're not made for it. Try experimenting and using other troops.