Composition
There are five basic rules of composition that are the essentials for a good photograph. Of course you will not be able to use all five in every photo, but the more you incorporate, the stronger your photograph will be. These basic rules, that may seem to be common sense for the most part, are overlooked many times because we have "selective" vision. If you make a conscious effort to see and use them, they will soon become second nature to you and you will automatically know if the photo you are about to shoot is composed properly or not. Of course, these are not always static and you may choose to "break" them for an effect or mood. The five basic rules are:
Point of interest
Rule of thirds
Leading lines
Framing
Mergers
Point of interest - Simply, what you are shooting. You always want a strong point of interest. In the case of photographing people, it is pretty simple. In the case of things like wildlife, you may see what you are shooting perfectly, but then when you look at the photo, you have to look closely to find it. This is where the "selective" vision comes in. Your attention is drawn to it and you see it nicely through the viewfinder, but there is too much background or surrounding area that you don't notice, hence, it gets "lost" in the photo. Always orient your camera vertically or horizontally to suit the point of interest.
Rule of thirds - When looking through the viewfinder, divide your frame into thirds; 1/3 from the top, 1/3 from the bottom, 1/3 from the left, and 1/3 from the right. On or close to these imaginary lines is where you want to place the main focal point. If the subject is looking or moving to the left or the right, always have it coming or looking into the frame. In other words have it in the left or right third moving into the frame (see the photo below). Horizons should most always be in the top or bottom third, very rarely in the center of the photograph. If you are shooting a sunset or sunrise, have the horizon in the bottom third. After all, you are wanting to show more sky. If you are shooting the land or water, you'll want the horizon in the upper third.
In the event you are photographing people, if full length, you will want the upper chest/shoulders in the top third. If photographing half length, the neck area should be in the top third and with head/shoulders shots, the eyes should be in the top third.
Leading Lines - These are anything natural or manmade that "point to" the subject. This can be anything like a fallen tree, a road leading to a sunset, railroad tracks, etc. In the photograph below, the railroad track serves as a leading line to the subject.
Framing - Framing is anything natural or manmade that breaks up the edge(s) of the photograph and brings your attention into the point of interest. It can be something as simple as a tree branch or even a wall to break up a border. In the image below, there is a tree on the left and some branches on the right that "frame" the waterfall in order to draw you into the photograph.
Mergers - Mergers are almost always bad and should be avoided. Some are very blatant, such as clashing colors or clashing patterns, but some are easily overlooked like the horizon that goes through someone's neck or head. Another one that is overlooked many times is when photographing someone in front of a tree or bush. Always notice the foliage behind the subject. If shooting at a higher aperture where you get more depth, it will appear as though the limbs or branches are growing out of the subject's head or body. Also be aware of hands especially and show some of the arm or it will look like the hand is growing out of a body part where it shouldn't. This can be particularly annoying if you are photographing couples.
All in all, be aware of the position and orientation of the subject and the surroundings. If you consciously practice these basic rules, in no time at all, you will automatically be aware when something does not look right.