This guide is work in progress, but as I read through a couple of other guides, I felt some crucial information was missing, so I didn't want to delay the publication!
With that out of the way, let's do it!

This guide was written during the version 4.23

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The first steps might the be among the most intimidating - where to build a base?
What buildings to get from the first money you get?
Can you completely fk up your run in the first few minutes?

To answer the last question first, yes you absolutely can!
For example by building your base in a location where the radar wont cover a lot of landmass.
My standard building is in northern Africa, to cover Africa and Europe with the radar,
but Central America and South East Asia work as well.

Now, what buildings to get first?
First, get a third hangar (to get a second interceptor in there),
a generator,
a second radar,
and a medical center. You could go for a training center instead, but the healing and the occasional cheating death seems more important than a little training (remember you need to research aliens and use their corpses in engineering to get a better training rate!).

The first mission is crucial, and when I am playing Ironman, I basically start a new game if the first one doesn't go as it should.

Basically, what you need to achieve here is
A - stun (not kill!) the enemy leader - which will give a boost in finding the cleaner base.
B - stun at least one Cleaner Agent - which will allow observation research of cleaners, giving bonus monthly income.
C - recover as many Cleaner bodies and weapons as possible - which can be sold after the mission.
D - try not to lose too many (or any) soldiers in dead or heavily wounded.

To achieve A,
you need more flashbangs than you would've brought otherwise, and more stun batons.
A simple trick is to load up one guy (who you will not need in your first round after deployment) with flashbangs and a stun baton, to the very brim of his backpack, ignoring that he will have zero AP.
In the first round, drop all the stuff on the ground and proceed as usual.

Before entering the final room (the one with the sand bags in front), go back to your entry point, get the flashbangs and the stun batons, distribute as appropriate (give the batons to the guys with the highest reflexes! Melee weapon hit chance is based off reflexes, not accuracy stat), and proceed with the breach.
The ideal breach looks like this:
Two shield guys in front, open the door, flashbang the general, flashbang and kill the agents, close the door.
Next round, open the door, flashbang the general, use a demolition charge to destroy the table be hides behind (so your stunners have a shorter path), run in and stun.

For B, just suppress one enemy close to one of your stunners, and stun him.

For C, don't use too many grenades / high-explosives, otherwise all those corpses and their equipment get lost.

For D, play slow and careful.
You don't have a time-limit.
You don't have to save civilians.
There are no enemy reinforcements coming.
Set a team around a door, let a shield bearer open it, let others shoot through if necessary, and close it again.
Rinse repeat until no more enemies appear.

After the first mission, research the "Observation: Cleaner Agent" and autopsy, then start aerial combat and wait for the UFO.

Shoot it down, play the mission (do NOT just take the money, you need the alien materials and equipment to get your research going!).

I strongly advise against researching Combat Vehicles, because those are quite expensive for what they bring to the table, don't get experience / skill level-ups, and are still rather fragile.
Also, you don't have the time.
You always lack the money, so you need to finish as many "+monthly funding" research as possible until (the end of) day 30 (60, 90, 120, ...).

My standard combat team setup (9 man) looks like this:
One or two shield bearers, two assaults, two snipers, two or three riflemen, and one heavy or grenadier.

Different mission types change my setup though:
For ambushing the Cleaner convoy for example I bring two heavies to kill/wound/suppress a bunch of enemies at once;
For extracting the VIP, always two shields to keep him alive easier.
For killing the enemy VIP, two grenadiers - as stunning and extracting him seems unfeasible in Commander Ironman, I put two snipers on containers, use the HEVY launchers to destroy the walls of the building where the VIP hides, and kill him with snipers.

Sort by Str, strongest become heavy / grenadier (if their Acc is not too horrible) - helps with recoil, and holding extra hevy mags.
Sort by TU, the least (!) mobile become snipers (if their Acc is not too bad) - they don't need to move anyway.
Sort by TU, the most mobile become assault - they need to move a lot. Ideally, they also have high Reflexes, so they hit their stun baton swings. Otherwise, you can give your best RFL soldiers the batons before going into the rooms with the high priority targets.
If you need to bring wounded soldiers or ones who cannot wear heavy armor, give them the shield role.

If you play with armor-destroyed-on-death, you will most probably be short on armor, always.
In this case, priority should be given to your most valuable highest ranking soldiers.
I always give the heavy version of every armor to all my soldiers, ignoring the penalty to accuracy and counteracting the higher weight by giving fewer grenades.
My ideal is giving heavy guardian to every soldier no matter the role.

The weapons are not just better and better, like in UFO 1 and 2, but the different tiers have different advantages.
So, accelerated weapons are in general stronger than the starter ballistic weaponry, with higher damage and higher armor penetration;
Lasers go back to ballistic levels of penetration (mostly 0), but destroy a lot of armor, plus they give bonus to ACC for people with low accuracy stats.
So while usually I just give the best weapons to the best people,
Lasers go to the soldiers with the lowest ACC stats.
Also, your lasers very effectively destroy environment and can later be upgraded to recharge.
This makes them useful even late game to have, to destroy woods, walls, stones, ...

Grenades are incredibly useful in this game.
If you've ever watched UFO 1 playthroughs, where the first grenades fly out the troop transport even before a single foot gets set outside, that's almost the level of throwing we want to achieve:
If any enemy looks even remotely towards you, flashbang him.
(For Mantids: Flashbang no matter where they look)
If they hide behind cover, and you dont have a spare Laser shot to safely shoot it, use a charge to destroy it and wound the enemy behind (unless it is wounded already and you fear to gibb him).
You left a guy exposed in the middle of a field? Smoke him!

Modules are items of size 2x2 which give certain bonuses to the soliders carrying them, like higher accuracy, immunity to gas, hp regeneration, higher str, increased TUs etc.
Id advise to give your shields and assaults the gas mask, for they are most often the ones having to run through smoke,
Aiming module to riflemen, snipers (if nothing else seems useful), heavies (if they have enough ammo).
Mid-game and further, hp regeneration module is useful on all your soldiers, even the riflemen with their medikits.

Stun batons go on my assaults (unless its a mission where I know I wont need them, like an escort - it seems unfeasable to stun someone and then carry their bodies to the helicopter).
Stunning aliens which you already have stunned and recovered is still useful, because living aliens sell for more money than corpses (once you sold a bunch of corpses and their price went down).


Personally, I've never used knives, neither the normal nor the upgraded versions.

As for starting your research, I would advise to research the Cleaner Autopsy first, as it gives your engineers something to do, and Cleaner Agent observation afterwards, as it gives both +250k funding and 15% damage bonus against cleaners, who are your main enemies at the start of the game.
After that, Aerial Warfare is important to get the Air-to-air missiles before the first UFOs arrive.

Right about now, your first mission should occur, and if you don't blast all your alien enemies with high explosives, should recover lots of items, allowing new research.

Here you'll get introduced to a reoccurring dilemma: Research useful tech like weapons or armor, or plot tech which increases funding?

I'd research useful first, and funding-increasing topics right before payday.

At the end of the month it doesn't matter if you did
Xenobiology -> Magnetic Weapons
or
Magnetic Weapons -> Xenobiology,
but in the first case you would get the weapons 9 days later than in the second case.

Main question here is what you prefer to get first, better weapons or better armor.
I usually go for armor, because I don't like losing troops, while having to spend a shot more to get the kill is not a problem, usually.

If you somehow managed to capture a live cleaner soldier (the ones in the overall), you should probably research him first, then Xenobiology, and then weapons/armor (which will take you into your second month).

After researching AA weapons, you have to build them too;
And after your hangar got built, build a second interceptor ASAP. If necessary, sell some of the loot.

When playing on commander difficulty, auto-resolve is no longer an option, so ideally you should master it before starting that mode;
But even of easier difficulties, you can do better than autoresolve, usually, and here is how:

First, you need the right amount of aircraft - the more the better, and one is not good enough for anything beyond the first few sorties.
I usually only have two aircraft, and that's fine, even though three are better, obviously.
And you absolutely need the best explosives researched to get the most bang out of your missiles and torpedoes - this is among the highest research and production priority for me.

Now, what to equip?
For heavy UFOs, you need two torpedoes and a missile per interceptor,
for light UFOs (which can do evasive rolls), a gun and two missiles.
Before UFOs appear, you obviously don't know which ones will come, so - equip gun and missiles.
The reason is that changing to torpedoes and missiles is a much faster rearming process than the other way round.

What to do at the start of the fight?
Unless you're up against fighters or interceptors (who attack you first), you can decide on the formation (top left corner). Coming from the front is usually the worst possible way to fight. You might be good enough to win, but other formations are almost always better.
Also, click on your torpedoes or missiles to prevent your planes from shooting them too early.

I usually go one from left one from right side. This forces the UFO to turn towards one of the fighters. Once the UFO starts to turn, I slow the aircraft which the UFO starts turning towards down - if done correctly, the UFO turns towards the other.
Ideally, you can change which plane goes full throttle and which one brakes, turning the UFO left and right, letting your planes come close without the UFO actually turning its front to a plane.
Ideal never happens, but even a bit of turning can help.


As for your missiles and torpedoes, against light UFOs, only use missiles, and torpedoes if you don't have heavier targets, and from close range, and right after the UFO did its evasive roll.
Against heavy UFOs, shoot all our torpedoes instantly at the beginning of the fight, and missiles only after the torpedoes hit and destroyed the UFO armor.

One more thing - shortcuts are your friend here:
F1 is pause, F2 is time going slow. Never play faster.
1-3 is choosing your aircraft.
Q and E is evasive roll to left or right.

The Xenopaedia tells us that equipping Torpedoes makes evasive rolls impossible: This is a lie. Use it as usual.
Ideally, you roll right before the enemy missile or shot hits you - this way, there is a chance you evade a second shot as well!
A great thing about pause is you can give commands. So, before getting hit, pause, give commands, unpause.

If you cannot afford those advanced airplanes, don't worry, the very first interceptors are actually not completely useless for late game:
Just equip them with two torpedoes and one missile, and let them fly in packs of three -
As long as you researched the best available warheads, they should be able to shoot down even the heaviest of UFOS - if, that is, they catch up.


If you didnt bring enough missiles / torpedoes / planes to down a UFO, you can just shoot what you have and retreat. Get back to base, reload, and fight again.

You lose the game if two continents abandon your organisation, so staying in your base and covering two out of the six continents wont do;

So, when to build a second base? And where? And what to build?
When is a hard question. I advise against the beginning of the second month, even if you have the money - you need it for lots of other things...
Beginning of the third month, or even slightly before, seems more reasonable to me.

Where?
Again, somewhere around the equator, to cover both North and South America or East Asia and Australia, or Europe and Africa, depending on where you have not started.

What to build?
Next to the elevator, a hangar, a radar and a missile battery.
Final goal should be
2-3 hangars,
2 radars,
2 batteries.
You can try to go without missile batteries,
counting on your planes to intercept any enemy ship coming for "retaliation" (attacking your base), but I've lost far too many bases to aliens when my interceptors were on their way shooting down a different UFO,
or the interceptors just being too slow to intercept...
Also, keeping a squad in the base just for defense is far more expensive and too much hassle.

Build two batteries and upgrade them and you're good!