Basic Game Play Strategies
XCOM®: Enemy Unknown Guide
The secret to success in playing EU is in knowing - and following - the rules. The reason for that is as simple as the rules themselves as those rules are what keeps your troopers alive and injury-free.
Rule #1: COVER, COVER, COVER!
In the world of squad-based tactics and strategy there are rules you always follow no matter what, and the reason that this one is Numero Uno is because it is also the most important. Moving from cover to cover is the best way to prevent your trooper taking a hit or getting killed.
Avoiding wide and open spaces is also a good idea, as is finding a route from one cover to the next that is itself covered.
Rule #2: Overwatch is Our Mate
When you find yourself in position but with no bloody idea where the alien enemy is, THAT is when Overwatch is your best mate! You can hunker down, place your troopers in Overwatch and wait for the enemy to reveal themselves.
If they move into range your troops will automatically fire - if they scan you get an idea of the direction that the threat is in while still set at a trigger-ready response level.
Rule #3: Situational Awareness
Another critical rule - knowing what is going on around you is key to mission success - particularly thanks to the scan system that the enemy uses.
When your troops are dropped into a mission, your priority is to establish Situational Awareness. You accomplish that by getting your team into cover and then seeking clues to the enemy location or direction. That comes with enemy scans or movement.
Rule #4: When Low Reload
Even in the middle of combat you need to keep an eye on ammo levels and, when there is a lull or it is safe to do so, reload even when a trooper is not dry.
Rule #5: Save your Med Kits
While it is a good idea to have at least 2 or 3 of your squad to carry Med Kits and an even better Idea to have one of them pursue the healing Medic profile, it is a bad idea to actually use those kits during battle unless you absolutely have to.
What this means is simple - getting wounded is NOT a reason to use a Medkit. Getting incapped is. You save those for when a trooper gets downed, not wounded.
Once you reach near the end of the mission you can use the kits to heal troopers that you know you can fully heal (that will keep them from ending up in the infirmary)
Rule #6: Overlapping Fire
Believe in the protection of your fields of fire - and try to always have each trooper defended by the overlapping field of fire from one or more of their squad mates.
Conclusions
Adopting the strategies outlined above you will quickly find that you can not only defeat a superior enemy force, but you can do so while keeping all of your squad alive.