I also just remembered the crappy "motion sensors"... A lot of people take those motion sensor for cash... But in reality, they are more often an hindrance than any kind of help.
The motion sensors will only show you something which has moved the previous turn... It won't help you to find Aliens which didn't move at all. Not only does that happen often for Aliens but you could also fall on a case of an Alien panicking and doing nothing but losing all its APs... Which will tend to happen a lot after you have killed its 12 or so friends. The motion sensor won't help at all in such a case.
Another problem a lot of rookies have is that they don't understand how the LoS works. You need to right click around to make your squaddie look around, and every tick cost you one AP. A lot of rookies end up passing by Aliens because they supposedly want to "save on AP" that way... And either end up dead or miss aliens which now run amok behind the squaddies line.
Xcom is really a gem: easy to play but night impossible to master.
