Here are the basic tips in combat for XCOM 2. XCOM 2 is known to be brutally difficult to players who are careless in deploying his / her squad in the battlefield. When the soldier is revealed by stepping into the perimeter of sight of the alien forces, the player gives up a lot by losing the chance to ambush the aliens. In short, do not blitz across the map, take your time, but also mind the missions with “turn limits”.
Overwatch allows the soldiers to take a free shot of aliens moving within its range. The overwatched soldiers always shoot at a single target until it dies, given that the target is within their range. Remember, concealed soldiers will never shoot even when overwatching, not until his / her position is revealed.
Overwatched units have penalty in their aim, UNLESS, it is an ambush. An ambush occurs when the aliens are attacked upon breaking of concealment. There is no penalty in aim for this. So never break your concealment until you have great advantage in positioning. Aside from the obvious actions that break concealment, below are some additional actions that gives up your position.
1.) Throwing utility items (mimic beacons, proximity mine, grenades)
2.) Hacks
3.) Psi abilities
4.) Patrolling aliens
It is rather predictable that you would break concealment as soon as you see a squad of aliens. Let it go, make sure that you are in the better position, and the aim percentage is at the high 90’s. There are only a few soldiers that can go back to being concealed (or starts at the mission concealed during specific missions where you arrive hot). Rangers have the ability to become concealed once more, and this can also be learned (albeit randomly) by other classes through the AWC.
Concealment can also be retained even though you are within the range of sight of the aliens, given that the soldier came there first before the alien’s sight flowing all over and the soldier is hiding even in half-cover. However, that soldier cannot take actions other than overwatch or hunker down, or else the position is revealed