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Hey OP fellow abandoned mine/urban explorer here, while the slogan "stay out stay alive" always applies to abandoned mines there's more to it then that. You should be especially wary of mines that are partially flooded or have a lot of moisture/water in them. Puddles and flooded floors can easily conceal winzes (vertical shafts that can go hundreds of feet) and false floors (pits or dugouts concealed by almost always rotting or structurally unsound wooden planks.
Also if you stir up that water you can release poisonous damps (mines gases) or find yourself in low oxygen environments from oxidation of rusting or rotting wood and metal. There's no way to tell without a gas monitor and you can pass out before you can escape.
Gold mines out west tend be much safer in this regard because they usually don't have a lot of standing water.
