This section is devoted to the various maneuvers that can be used on the battlefield in order to minimize loss of life and help eliminate what more resistant aliens. It assumes that we conduct research on an ongoing basis when new types of aliens appear and that we have assimilated the basic information about the gameplay mechanics in the tactical game.
One of the basic maneuvers, which are used in the initial phase of the battle, is getting the correct unit when you do not yet have detected the enemy. As mentioned earlier in the section Detecting opponent, one of the key steps is to know the size of the map where you are, and any attack path of the aliens. After this, the next step is to find a field shield behind which we can hide the soldiers. I would recommend to turn first to those who are just one move, saving the second action point to a possible exchange of fire with aliens (if we are unlucky and aliens were close) or Overwatch mode (if we have not yet discovered the enemy).
The next step is to choose one point (preferably at the edge of the map) and moving in its direction. We should always start with a single point of soldier's action, saving the other for when the enemy appears. I do not recommend running blindly using both action points - a soldier is exposed to fire, and his death could cause panic and his companions continued loss of life. In the first phase of the fight very useful is the ability of the sniper: Battle Scanner. Thrown like a grenade, it reveals invisible so far for us the area - this is a really great skill reduces the risk of falling into the trap in the first few rounds of the game.
Sooner or later, we detect a cluster of aliens who hide behind the nearby obstacles. At this point, the saved action points become useful: soldiers located at the back can shoot aliens (especially useful here are rocket launchers and sniper rifles), and the Rangers closer to the enemy can choose between throwing grenades or running Barrage hiding behind obstacles (Hunker Down). If the opponent ran us out of the field of view can also be used Overwatch mode - but he has some huge flaws. First, enables the soldiers to shoot with a reduced accuracy, not only wasting ammunition, but also losing a movement (if an alien stopped in an open area, a normal shot would be more effective). Second, it often happens that if you set the number of soldiers in Overwatch mode, everyone would give a shot to the same alien. This ensures a better chance to kill him, but the other two aliens can escape from our attack. Personally, I recommend using only Overwatch mode with a Sniper (before you reach the maximum level of experience and will be able to give two shots per turn), Heavy with the ability to Rapid Reaction and Support with the ability Sentinel. The remaining soldiers should rather save action point to perform a normal attack.
During the fight we shouldn't attack blindly. Aliens often try to get closer to our soldiers, and therefore they can be drawn into the trap, if the soldiers withdraw from the first line of fire. In addition, it gives us a wider room for maneuver, because the use of the skills of the Assault class - especially Run & Gun - on newly discovered alien may help us discover another alien group. But if we use it after the retreat, we will return to previous position without the risk of stepping on a larger enemy forces.
Another problem we may encounter are aliens hiding behind heavy terrain barriers. As far as possible we should use an outdoor area for flanking them. If this is not possible, I recommend you just change the terrain using grenades and rocket launchers. If the enemy is hiding behind a car wreck, the situation is even simpler - you can go ahead and attack him. Some missed shots set fire to the vehicle and the next round will be an explosion that will kill aliens. We have to be careful, because it works both ways - target shooting aliens may ignite our cover. It is then time to withdraw the explosion, and later you can go back to the previous position.
In addition, we can use the terrain. Shooting from a higher position increases our chance to hit, so the Sniper or the Support class on the roof have a much easier task to shoot on an opponent behind the cover. Approximately in the middle of the game we will gain Skeleton Suit armor with built-in grappling hook - just select the appropriate capacity and aim at the above location located and our soldier change its position. As the alien (except for Floaters) rarely use rooftops as sniper position, it allows us to flank most of the opponents. The attack from the flank in conjunction with a dominance from above will quickly end each turn.
Fighting within closed spaces (e.g. foreign ship), we should wait 1-2 rounds opening the door and set up the so-called firing squad, i.e. two soldiers along the edges of the door, the rest directly in front of them. We set a number of soldiers in Overwatch mode, we open the switch and watch the scene. Typically, one or two will kill newly discovered alien already in the preliminary clean up, while the rest we will kill with the Assault class or (less often, because you can destroy valuable items) throwing a few grenades inside. Surprisingly, the most difficult task for a soldier - entering closed rooms - in XCOM: Enemy Unknown is extremely safe and easy.
We should also remember about using military skills. Despite the fact that dead alien is not able to harm us, will not always be possible to eliminate all opposition. A well-thrown grenade with the ability Dense Smoke is as effective as the hard cover - a soldier in the open air suddenly becomes very difficult to hit. Suppression not only reduces the accuracy of the enemy but it gives us the opportunity to fire when he moves. In conjunction with the ability Danger Zone of the Heavy class, we can virtually exclude from fighting the alien group.
At the end: armor. It increases the number of life points we have on our marines (most importantly, the armor gives 5 ??points of life, so only after receiving 6 damage will cause the soldier to be hospitalized!) and often provide access to unique abilities: the aforementioned Skeleton Suit and its grappling hook, the ability to fly, or to become invisible - armor is just as important as modern weapons.