Many amateur photographers seem overwhelmed in the field with their camera and simply finding something to shoot. I have found over the years that every scene we photograph can be divided into two categories. It is either an f-stop controlled photo or a shutter speed controlled photo.
F-stop controlled photos are those where you either want great depth-of-field with foreground to background in sharp detail1 or the opposite which is a complete lack of foreground or background detail and only one subject in sharp focus2.
The larger aperture openings (small f-stop numbers such as f-1.4, f-2 etc.) are used when you are photographing a single subject and you want the foreground and background completely out of focus3. It's called selective focus. This is an effective technique because it forces the viewers attention to the subject you want them to see.
The smaller aperture openings (large f-stop numbers such as f-16 and f-22 etc.) are used when you want everything from only a couple feet away to infinity in sharp focus4. This is called depth-of-field. This is helpful when you have close up detail5 and a subject that goes to infinity.
Sun stars6 are a function of the diaphragm blades in your lens and can really add interest to an otherwise uninteresting subject. The best stars are achieved when you use the smallest aperture of your lens, which is usually f-22, and a shutter speed equal to the ISO being used. Try bracketing your shutter for different densities. Using ISO 100, your exposure would be 1/125 sec. at f-22. Letting the sun "peak" between the leaves further increases the effect and minimizes any flare in the lens.
Shutter speed controlled photos are those where the speed of the action of the subject is most important. In foliage photography, you need to always use a shutter speed fast enough to stop the "quaking" motion of the leaves in a breeze or long enough to allow rushing water to become a blur for a more pleasing effect.
Water blurs7 are achieved by using a long shutter speed, usually somewhere between 1/2 second to 10 seconds. The longer the shutter is open the more the subject moves and the greater the blur. Check out the photos8-11 for the degree of blur that you like best. Faster water needs less time to show motion.
To achieve these long exposures, you will need dark neutral density and/or polarizing filters to really cut back on the daylight. Remember, the polarizing filter uses 2 stops of light and also minimizes the reflection of the sky on the water. The impact a photo like this delivers is why this technique is a valuable tool to learn for shooting in the shade or on overcast days.