I don't know if this is a bad advice or a good one but it's what I personally do when I play on sanhok. Don't ever stop moving around, crouching or running on zig zag or jumping but don't stop moving, and try to use the many trees and rocks as cover while you're moving, so if an enemy spots you you'll be able to get lost easily and now spot him because he gave his location away already. And for spotting enemies, all I can tell you is to have good reflexes (to react first and faster than the enemie), headphones on, and look carefully and fast around you, you have to examine quickly your surroundings CONSTANTLY and if you see a little tiny suspicious thing, get closer (looking for cover as well) and have your gun ready, if you're playing on Squad tell your teammates to surround the enemie.. don't go all four in a straight line trying to rush him.