This is a look at how to specifically develop a very powerful early game based on the mechanics of ranged combat, particularly the Overwatch feature.
If you've messed around and tried melee units you may have seen how they can get horribly shot up on their way in to where they need to be. This is, sadly, because melee sucks in the early game. Later on when you have heavily fortified teleporting or jetpacking units it might be a different story but this is the melee vs ranged scenario:
You move in. Opponents take overwatch shots against you. You reach the bad guys with about 1 action point left and do one third of what a full round of attacks would do. The opponents shoot you. At this point they may have had 6 attacks to your one.
So it's a no brainer to play ranged, right? Sure but there are two issues - you need to force defending enemies to engage and the overwatch UI is a little unintuitive. Don't worry, here we'll solve the first issue by making a sniper - if they hang out and do nothing you can snipe one shot per turn and that'll wake em up. And I'll explain in pictures how to set up Overwatch.
Start a New Game (Scenario or Campaign, it doesn't matter).
(Optional) change Opponent Level to Very Easy. If it hurts your ego you can always come back later and make a new game on a higher difficulty. Or you could try it on Normal or something and see if these tactics are enough to get you through.
On the next screen choose Customize Commander.
You need a race whose default units are decent ranged troops. So far the best I've seen for this strategy is Vanguard.
As for your Secret Technology I honestly don't know yet which one is best but it doesn't matter too much as our crucial mods are in other tech lines. Voidtech seems to be for enhancing melee so that's probably not a great one. Other than that just pick one you want to try.
Pick Martial Tradition, none, Vanguard Sharpshooter Equipment, none as your perks.
Customize him/her however you like.
Scout with both OWL scout units (leaving you with a 5 stack as your main army).
Build Central Replicator Factory and Vanguard - Trooper at your colony.
Move your army out to clear a nest of bad guys, no more than 3.
Use Manual Combat.
If the enemies rush into range then you can back off a bit and set up an Overwatch trap. Normally they won't be in range in which case we'll move the sniper commander one green square closer then set him on Overwatch.
To set overwatch press the overwatch action key (5 for the guy in the picture) then with the zone highlighted in purple right click. You don't have to do facing first as it automatically adjusts facing.
|Right click in the purple hexes to set overwatch|
Form your troopers in a gunline and set overwatch. In the example I've actually used a couple of them to clear an annoying obstacle instead of leaving them on overwatch. (Mostly because I don't think these particular enemies will rush into my overwatch zones next turn).
|A gunline perpendicular to where the enemies will come at me.|
|The serrated white line shows the edge of sniping range.|
In the picture it's a pretty low hit chance shot but it doesn't matter. The purpose of this shot is to provoke them and make them come charging out.
Here is the same time in the battle showing my gunline. My PUG has dropped a Blur Cloud on the trooper in front of it.
The bad guys move forward, triggering two troopers who fire overwatch shots into the bike. Look how badly damaged it is. This means our sniper commander can shoot it and because of the perk he chose he'll get another go if he kills it. One of their other units picked a good position at the edge of shooting range and got a couple of shots off, not triggering overwatch. His last unit pointlessly entrenched miles away from the action.
|Position at the start of round 3.|
Unsurprisingly the sniper kills the bike but sadly he misses his shot on the enemy trooper. I push 3 units down that flank to get enough to kill that trooper without anyone getting in range of the entrenched unit at the back.
I retreat my sniper one hex to take a snipe right on the edge of max range while moving the others to form a gunline back near where I started, putting them all on overwatch. My PUG uses its medkit on a damaged trooper.
He managed to get a good hit on my PUG as I'd stupidly left it facing sideways so it got flanked. Note to self - position better next time. But it's too little too late as I take my snipe then move my troopers up to finish it off.
So take your time early on and don't take on battles when your guys are wounded. If you look after them they will level up which gives them more hit points, accuracy and a skill: Improved Overwatch.
I got them all up to their maximum Trooper level in one game without ever loosing a single trooper. It gets a lot easier once they have experience and mods and once you get the stack up to 6 units. At that point I could auto-battle against stacks of 3 npcs and come away with barely a scratch.
It works even better against melee. I did a battle where the melee enemies moved quite badly and basically came in one at a time and they didn't land a single attack, dying to overwatch zones and sniping before they got to my guys.
You will also want to mod them when you can.
I like Nanite Injectors. This gives them a heal which I usually use at the start of combat as not much usually happens in round 1 so it means I can go in injured and be on full health when the action starts (and often still on full health after the battle.)
Ammunition is good, Ammunition - Flechette is fine.
Rail Accelerators gives you an extra range which is very powerful for this strategy as we're usually fighting at max range.
I hope this works out for anyone new and feeling a bit overwhelmed and perhaps some of the grizzled vets might pick up a thing or two.
Good luck and have fun!