There are patrols, not on all maps, but most crashed UFOs have them. And yes, overextending yourself is a classic newbie error. Unless there's a turn limit on screen, you have all the turns in the world. It's not like in the original where the aliens gained map-wide Squad Sight on turn 20. Fun with the classic "no line of sight needed for Mind Control" Ethereals.
Anyway, the ideal move is you have a scout move ahead first, if he spots something, do an appraisal. "Can I kill these before they get a turn?" That's not always a guarantee, but it is the ideal. If you're overwhelmed, fall back and set up an ambush. Aliens will NOT move out of cover into Overwatch, but that's only if they've seen the Overwatcher go on Overwatch. A Sniper with Squad Sight is a great Overwatcher as it can fire from outside visible range.
By the way, I just gave you a hint to an interesting AI quirk. An alien will not trigger Overwatch if it knows. But an alien will also want to get into cover if it is not. So riddle me this: A flanked Muton is being watched in Overwatch. What does it do?
This also works if the aliens are out in the open, so blow you their cover and and go into Overwatch on them. It's a bit of a cheap shot, and some aliens do act differently, like Chryssalids that happily charge into gunfire, but know your foe.
Anyway, the ideal move is you have a scout move ahead first, if he spots something, do an appraisal. "Can I kill these before they get a turn?" That's not always a guarantee, but it is the ideal. If you're overwhelmed, fall back and set up an ambush. Aliens will NOT move out of cover into Overwatch, but that's only if they've seen the Overwatcher go on Overwatch. A Sniper with Squad Sight is a great Overwatcher as it can fire from outside visible range.
By the way, I just gave you a hint to an interesting AI quirk. An alien will not trigger Overwatch if it knows. But an alien will also want to get into cover if it is not. So riddle me this: A flanked Muton is being watched in Overwatch. What does it do?
Nothing at all. It skips turn.