Minecraft wiki entry for Exploring_an_ancient_city, associated text: Try not to build or destroy anything unless you are sure there are not any Sculk Shriekers or Sculk Sensors within a 9-block radius.
Try not to take any damage, keep your health bar at full, just in case.
Try your hardest to avoid alerting sculk shriekers or sculk sensors, so do not step on them, let alone go anywhere near them except to break them.
Do not try to fight the Warden under any circumstances! It will kill you! Instead, try to be as far away as possible, because it may detect your presence the closer you are to it and be able to track you down, with fatal results.
Do not place anything, including Wool, on top of Sculk blocks, as this will alert them and they will then notify sculk sensor nearby, preventing you from occluding them.