Wet rocks and logs are by far the biggest dangers to the hiker. Crossing streams by rock-hopping is the biggest mistake any hiker can make. Any rock that looks remotely damp is usually covered with a slime that is slicker than ice. Look for spots to cross where the stream bed is mostly gravel. By realizing the dangers ahead of time, many potential problems can be avoided.
Experience is a wonderful thing.
It allows you to recognize a mistake in that split second before you make it again. Clothing choices are another mistake many hikers make. I see so many people decked out in their khaki shorts, t-shirt, cotton socks and a pair of ultralight hiking boots who look like they should be on a promotional poster for the Swiss Tourism Bureau. The problem is they will encounter some obstacles such as stinging nettle, briars and branches on many of the trails which are now overgrown with lush vegetation. Not to mention what the sun and wind exposure can do.