Fish want to live a comfortable life, just like we do. They want protection and they want food. If the water we are fishing does not provide these things it is unlikely that there will be fish there.
One of the most common mistakes I see fishermen making while fishing rivers and streams is that they are fishing bright water. We have to remember that fish don't have eyelids and when the sun is out the fish are going to look for some shade. If the water is clear the problem is even bigger.
Fish the areas that provide protection from the sun. These are the areas that fish will be hiding. If you are fishing on lakes the best protection a fish has from the sun is depth of water. Don't be fishing the shallow areas of the lake on bright sunny days.