Trigger Discipline Trophy
Complete a mission on Intense Difficulty or above without anyone taking friendly fire damage.Note: I strongly recommend having a Combat Rating of 650+, before attempting this trophy so your weapons do extra damage.
This trophy sounds hard but it really isn't, provided you do it during the mission "Priority One: Ingress" and follow these tips:
Do a dry run on Casual or Standard Difficulty: By doing a dry run, you can learn where the Xenomorphs will spawn and what the best postions are to place your turrent during the mandatory Swarm sequences.
Watch your HUD and use your ears: If you accidentally hit a teammate, you will see the following indicator on your screen and they will say "Cease Fire":
If you see this icon (which is a red triangle with an ! mark in the center), it's game over for the trophy so you will have to finish the mission then try again.
Play as the Technician: The Technician is the perfect Kit for this trophy once you have unlocked the Incinerator Turret upgrade, because then you can stand back and let it take care of most enemies for you. If playing in co-op, then have everyone play as the Technician.
Use a 4 star M37A3 Pump Shotgun as your primary weapon: Even though the Magnum can be pretty powerful once you have maxed it out, the small crosshair and magazine limits its effectiveness in most case so stick to using a 4 star Shotgun instead because then you will do maximum damage at most ranges (I recommend the M37A3 Pump Shotgun with the Precision Brake Muzzle, Drum Magazine and Hybrid Sight installed because 1-2 shots from it is enough to kill most enemies, even on Intense difficulty).
No explosives!: Shooting explosive objects is a great way to fail this trophy so don't shoot anything that's explosive. Also, make sure you don't have any Explosion based attachments equipped else they too will cause splash damage and void the trophy if a teammate gets caught in the blast.
Keep your itchy trigger finger off the fire button: If anything is going to screw you over and fail your attempt at this trophy, it will be an itchy trigger finger so keep your finger off and don't fire unless you have a clear shot that won't hit Alpha or Beta. If in doubt, don't fire!
Let Alpha, Beta and your Turret do most of the work: Alpha, Beta and your Turret are pretty resilient when left to their own devices so will take care of most enemies without you having to do anything. The elite enemies are the only ones that will give you trouble so take pot shots at them whenever you have a clear shot.
Stand back!: As I said above, your turret and AI teammates are more than capable of tackling most situations by themselves so stand back and don't intervene unless an enemy heads straight for you.
Don't Hip or Blind Fire!: Hip/Blind Firing just sprays ammo all over the place and gives you a high chance of hitting your teammates by accident so don't do it. You should ADS (Aim Down Sight/Scope) the entire time.
The End Zone: The hardest part of this entire mission is the final swarm that appears whilst you are waiting for the lift to arrive at the very end of it. The safest way to get through this final hurdle is to stockpile as many Hardened turrets as you can (either through finding them in chests during the mission or by purchasing them beforehand from SSGT Park in the Armoury onboard the Endeavour) then place them as per the following screenshot:
Once you have setup your defense perimeter, refilled your ammo and healed anyone that needs it, activate the lift then go stand on the left-hand side of the lift so no enemies see you. Once you get to approx 30secs remaining, a Xenomorph Warrior will show up so do your best to keep out of its way but if you're lucky and time it right, you can lead it into a merry dance around the lift then dive straight into the lift when it arrives and finish the mission without the Warrior ever grabbing you.
If you managed to finish to not hit either Alpha or Beta during the entire mission, this trophy and Didn't Break a Sweat will pop during the end of mission breakdown screens (that is if this was your first ever successful completion of a mission on Intense difficulty).
Here's an alternate method courtesy of enaysoft:
Pick the Technican and choose Stage 2-1 because the whole stage is lots of wide open spaces, I took in 3 Flame and 3 Electroshock turrets. Turrets don't do friendly fire, even if they are Flamethrowers and Electroshock. None of them deal splash damage or friendly fire and provided you put a turret down and cover the floor with Charged Coils, you can just lure enemies to your turrets. I did this with Alpha and Beta. Only hard part is near the end as you have two Big Aliens but that is when I used 3 extra turrets so I had 4 each. You can also pick up normal turrets in this stage and potentially from the hidden cache to possibly get even more.
Provided you stay away from explosive barrels when you place the turrets, it's impossible to have friendly fire since you just run around in circles around your turret and lure enemies in. I dare say it's even easier on Co-Op since everyone can bring in 3 Flame and 3 Electroshock turrets and two people have regular turrets and one as flame. When I had all buffs on turret and grenades, I was able to throw a Charged Coil every 10 seconds, meaning I had infinite fields near my turrets.