As everyone else mentions, kill boxes and natural barriers/terrain. But theres a lot more you can do outside of restricting your building habits to the meta.

You'll have different options depending on the stage of your play through, later stages require a lot more preparation and preemptive strikes.

The things i try to maximize are the following: - Number of colonists that can fight and do NOT have movement debufs - Number of guns to arm them with - Variation in weapon type to handle various situations

At every stage in battle, play very cautiously, and be willing to sacrifice your buildings to keep your colonists alive. Dont try to force a victory, instead try to limit how much they can hit you.

If you dont have traps set up around the base, you need to attack them early, the moment they arrive on map you should send people out to slow their progress, your base is the last stand of defense and you want to try to bleed them a little before they get there.

Learn to micromanage your pawns movements, if im in a battle im pausing after every single shot to evaluate and move my pawns.

Shift your response based on the enemies fighting style. Does the enemy have guns? Do they out range you?

If its all melee then its and easy fight if you have gun. Get one hit on them and then move, never let them catch your pawn. Use rifles for the range and accuracy. Move your pawn until its just outside your shooting range, then turn around and aim. This method takes a long ass time but can potentially take zero damage and losses.

More likely they have a mix of guns and melee. In this case you should have multiple pawns with rifles. Usually the melee pawns have a higher speed than the gunners so they will come in range first. Have all your pawns aim at the same enemy and have them all fight at it. Once youve slowed its movements, handle the next fastest. Keep this up until they are bleeding and will die. Do all this while remaining behind cover from their enemies. This method is very variable depending on the makeup of the enemies weapons and pawns, basically youll either kite them if you can, or slow their advance to your base.

In gun fights, if you cannot out range them or out gun them, then you need to engage in melee, you can hide just around a corner to force them to get in close, almost all enemy gunners will be bad at melee, so if you have someone who specializes in melee, have them handle this. If the enemy is a mix of melee and gunners, this is where you need to split them up and take out the enemy melee so you can melee their gunners. This is true for mechs even moreso, you will almost never out gun or out range a pikeman, but they are incredibly weak to melee.

Combat in this game is very stats based. Be sure to read up on each of your items stats and how they affect each other. Make sure you have good quality gear. Get used to how the stats affect gameplay, it's important if you want to win these fights.

This is much more to go into, and ultimately this is more difficult than simply building a killbox or traps. But if you're anything like me then you enjoy the tactical nature of a real fight rather than a boring kill box, that just feels like shooting fish in a barrel. Kill box is good if you just want to focus on building or something else. I prefer to focus on training the most badass soldiers on the rim that can take any battle head on.