This is a pretty straightforward strategy. You simply need to be on a map with a car (or have sentries if you are not).
So, the first method involves exploiting the carrier’s infinite ammo cannons.
Simply park the car near where your squad is and put down as many motion trackers as you like. If any Aliens start getting close, set one off, and they’ll run headfirst to their doom. Since motion trackers aren’t a finite resource, you can do this as long as you need.
If you lack a vehicle on the level you are on, you can replicate this with sentries if needed. (I recommend giving them a flare to help with accuracy from time to time).
Make sure wherever you put them cannot be flanked by aliens, or they will be quickly destroyed.
If any of the more stealthy sections are giving you trouble, just remember that both the turrets and the car do not cause a hunt when shooting Aliens.