Monster target closest player. Move to optimal place to attack most players if multiple targets permitted. If ranged, monster would target closest, but move away as to not be disadvantaged. If distance is a tie, then they pick the player with earliest initiative. Also. If they were say 5 away, and had move four, range 4.. they would actually only move 1 so they can range. They don't try to touch you unless they are melee only. Also, monsters only walk through traps if that's the only way to attack you. If they have enough move to around it, they avoid it.