Always position your soldiers on higher ground when possible. They will receive a +20 aim bonus against enemies on lower ground.

Enemies get the high ground bonus too so beware! 

Abusing the ranger's 'phantom' skill (which can be acquired early) is one of the best ways to approach XCOM 2's time-based missions. As long as you're careful not to break concealment, you can use your team of invisible rangers to move around the map to secure objectives while the rest of your squad distracts the enemy by luring them away from where your rangers are

In mid to late game, the toughest enemies you will face are Sectopods, Gatekeepers and Andromedons.

These enemies have high HP and armor, which makes them extremely tough. Even with a team 6 soldiers, its super hard to take down a Gatekeeper in one turn (if it has full armor).

You should have your Grenadiers learn the "Shredder" skill, which is a passive ability that destroys enemy armor.

Once you get an enemy's armor down to 1 or 2, it would be much easier for the rest of your team to take them out.

 

EMP bombs are devastating against mechanical units. These bombs do zero damage to organic units but wreck enemies like the Sectopod, Gatekeeper and Codex.

These little blue babies will deal around 10 damage (ignores armor) with a chance to Shutdown mech units for 2 turns.

If you get into a situation where you have 3 Codex's grouped up together, throwing one of these EMP bombs will destroy a bulk of their HP and most likely stun them.

So get these babies early and try to bring at least two on every mission.

Explosives are very useful in game.

Rockets and grenades destroy enemy cover, do guaranteed damage (they dont miss), and can damage several enemies in one blow.

However, you should not use them unless you absolutely have to.

This is because they destroy valuable loot on enemies. In every mission, enemies will drop Weapon Upgrades, Personal Combat Sims and Elerium Cores.

All 3 are vital to upgrading your soldiers and their weaponry. So kill aliens using your main weapon if possible.

Explosives will destroy loot even if it doesn't kill the alien.

Using grenades to destroy enemy cover so they can be flanked from your current position is better than having your squad run around enemy cover and accidentally pulling a fresh set of enemies from the fog of war.

Engineers are 10 times more important than scientists especially in early game. Get them asap.

You will need them to excavate the ship and man these facilities: Power Relay, Resistance Comms, Advanced Warfare Center and Proving Grounds. 

You will want at least 10 engineers when you reach mid game.

Engineers can be recruited in 3 ways:

• Resistance HQ* (bought using supplies)
• Black Market* (bought with intel)
• Missions (complete the mission successfully)

Always prioritize Engineers over scientists until you have 10 of them and a Workshop built in the middle of your ship.

Save your early resources for buying engineers from Resistance HQ and Black Market.

Get as many as you can in the first 2 months and you will have a much easier life battling the aliens.

Every point of armor reduces damage by 1.

If you hit a Gatekeeper for 10 damage, and it has 7 armor, it will only take 3 damage.

Shredding does not ignore armor. In your early attacks to shred armor, every point of armor will block damage.

Attacks that ignore armor include:

-EMP (only against mech units)

-Psionic (like Null Lance)

-Armor piercing rounds (ignores 5 points of armor)

-Poison

-Acid

-Fire

Best way to shred armor is by using Grenadier's shredder ability which is passive and free. (They suck at Aim especially early on. You can improve their aim by positioning them on high ground, giving them the aim PCS, upgrading their cannon with scope, learning holo targeting, and using tracer rounds)

 

 

Animations like reloading, evac, and gremlin heal/aid protocol can be repetitive and boring.

You can skip them by pressing "Tab" to skip to the next soldier.

 

Weapon Upgrades are carried forward from one tier to the next.

If you have a superior scope on your Magnetic Rifle, it will be carried forward to your Plasma Rifle. 

Don't sell all your trooper corpses in the early game. You need them to create Plated Armor and it's possible to hit a wave of missions without a single standard trooper. If you sell all those corpses for money and then hit a trooper-free mission wave then you will find yourself facing lots of high strength enemies with insufficient trooper armor. You don't want that. So just don't sell the trooper corpses and save yourself the trouble.