Fish like to see and not be seen.
Toward that end most fish like to relate to objects in the water or irregularities in the bottom that allow them to blend into the background. Fisherman call these objects and irregularities, "structure". Fish, by stationing themselves near weedbeds, rocks, fallen trees or in the shadows become more difficult to spot by other fish allowing them to ambush smaller fish and avoid being eaten by larger fish. If you look at most freshwater fish you will see that they have dark stripes or splotches on their sides that tend to break up their outline much as modern camoflage clothing does for soldiers. In addition most fish have bellies that are lighter than their sides sometimes even white. This is so that the fish don't show up so well against the sky when viewed from below by another fish..
Fish like to be near deep water
Most species of fish feel safer if they can retreat quickly into deeper water. Any place with a shallow area near a drop off will tend to hold fish. In shallow water fish tend to be more cautious and will spook easily, which requires greater care in lure delivery.
Where structure is scarce fish hang by the banks especially in early spring as the water warms.
In streams and rivers fish seek areas of slow to moderate current where they can wait for a meal without expending too much energy. These areas of slow current are on the bottom, along the banks, in front of and behind obstacles such as rocks and fallen trees. If they are actively feeding they will generally be facing upstream and into the current. In such situations it is best to cast upstream and bring the lure downstream to the fish. When the water is low fish are more likely to venture into the center of the stream. When water is cloudy and fast moving, fish like to stay near the bank or at the inlets of small streams where there are eddies and food opportunities
Fish are cold blooded creatures
Fish can be caught anytime of the year, however when the water is cold you will have to realize that you will not have as much success as during the summer. Since fish are cold blooded creatures their metabolism slows so they don't feed as often. In addition lure presentation must be slow, you have to make it easy for them to get the lure. Fish will tend to congregate in areas of the warmest and most stable water temperatures leaving large stretches of water empty of fish. However if you come across one of these congregations then the fishing can be pretty good.