Starting the game, your options are very limited since you only get Minis based on the Hero that you picked. By completing the quests, you'll be able to earn some gold so you can strengthen the ones that you have or get new Minis to try different compositions.
Getting new Minis can help with early game progression since they will give new quests, but you'll also need to consider upgrading units so they unlock new abilities to be used in battle.
Once you have more options and are in the higher levels, you can start to think about having proper synergy, the meta, and matchups so you can find ways to deal with them, as well as any balance changes that happen once in a while.
Understanding Your Win Condition
It's easier to build a deck around your selected Hero to bring out their strengths. A Hero like the Archer Queen is a strong damage dealer that can attack from range, so you can build a deck that can protect her by using many tanks/bruisers, or support her with some attack speed increase to carry the team. If you're using Shield Maiden, you can bring some ranged damage dealers like Archer or Dart Goblin to be the win condition.
In general, the idea is to make a deck that works well with each other and avoids bad combinations. A balanced team often has at least 2 frontline units and 2 damage dealers, but it's not always needed to go for perfect balance, especially since board placements also matter a lot.
To win a battle, you simply need to have more advantage than your opponent. This can be done by either boosting your team's strength or weakening your opponent.
Units like Dart Goblin, Archer, Wizard, or Valkyrie are examples damage dealing type units, just in different ways. Which one to use depends on what you're trying to go for.
Miner and Archer target your enemy's backline. You use them when you have good coverage for them and need some support from the back to deal with the enemy's backline, which are often their main damage dealers or support.
Wizard and Valkyrie deals damage in an area, which can be good if you use units with boast abilities or something like Swordsman or Royal Champion that can chain supers.
Electro Wizard is a good example of a unit that's both a damage dealer and great for disrupting your enemies. The downside is that it costs 4 Elixirs, so you'll have to consider if it's worth using compared to the other 4 Elixir options.
Effects like slows, stuns, knockbacks, or dissipates are ways to disrupt your opponent's flow, which can prevent them from getting an advantage over you. Which one to use is something that you'll know when you understand how to counter certain team compositions.
Prince has a clash effect that can knock back an enemy unit. This can be a great counter to an enemy tank to help your team or a way to get closer to the enemy backline and focus them first.
Bowler and Fisherman have powerful clash effects that can stun enemies hit at the start of the round. The risk is that you can miss them, but gives a really good advantage for you if you can land them.
Keep in mind that you don't want to use the Fisherman if you use a team of low HP ranged units or ones that go forward like Prince or Miner. This can end up causing you a disadvantage instead.
Ice Wizard has a slowing effect on each attack. This is great against enemies that rely on attack speed to deal more damage or gain energy to unleash their super.
Tanks are essentially high HP units whose role is to take the attention of enemy units and soak up some damage. They can be considered a way to disrupt your opponent since they slow down your opponent's advance.
Giant Skeleton is often used for a lot of different decks since it's good for soaking up some early damage and deal damage itself.
Golden Giant has a self sustaining ability when stunned so it can last longer on the field.
Units with really high HP like P.E.K.K.A or Mega Knight are also options worth considering. P.E.K.K.A has the potential to deal high damage, while Mega Knight has an area stun.
While a good amount of strategy is involved during battle through proper unit placement, there are definitely favorable and unfavorable matchups. A Hero like the Monk does well against the Shield Maiden, while the Shield Maiden can be good against the Archer Queen, etc.
Knowing how to deal with popular Heroes or decks can make things easier for you to adapt to the meta. You can find more details about each Hero's strengths and weaknesses on their own pages.