The AI is just shy. The aliens (assuming you are playing phalanx) will hide if you leave your soldiers looking at them during the alien round.
This means that (in a small way) you can control the enemy team. For example, it has been observed that on the dam map (dam01d) the AI will make its soldiers retreat into the building opposite your start location. This makes the final approach to the building tricky, as it is not possible to move from the nearest cover and get inside in one turn. Your troops are always injured (maybe killed) as they approach the last building.
So, if you ensure that the open ground in front of that building is not in any of your soldiers field of view at the end of your turn: the AI keeps its troops out in the open making it easy to shoot them.
One word of caution - you have to make sure you have RF angles covered, so they cant sneak up on you.
In a recent experiment, popi and I (coop2) found that we only had 2 enemy left (out of 8 ) in that small building. one was killed with a nade as we approached, leaving the last survivor panicking.
I have also used this tactic on other open maps (eg druglord).
If you want to keep your foes out in the open and easy to shoot, don't look at them!