Why plan Composition?
The reason why we as artists should learn to plan our composition of a art piece is so the viewer's eyes are directed to the important focal points of your piece. It's very easy for you as the artist to know what parts are important for you in a piece but if you don't lead your viewers eyes to it they will not perceive it as a focal point of your piece. I will go through some of the different ways of composition and show examples where they are used.
Divine Proportions
"The height of a well proportioned man is equal to his out-stretched arms"
-Marcus Virtruvius Pollio
The Devine proportions, or "The golden ratio" relies on the ratio 5:8. This is seen as the perfect ratio for proportions to be seen as most realistic and perfect by your viewer.
Human Figure in a Circle by Leonardo Da Vinci
Devine Proportions can also be constructed by using different shapes such as squares, triangles and rectangles. I will now go through some of the different structures you can use to properly plan composition for your artwork.
Root 2 Rectangle
In this one all the shapes are proportional. Where the dotted lines intersects is where the eyes are led to.
Root 3 Rectangle Spiral Construction
This way attracts the eye to the key focal point by using the minor focal points of the image.
Root 3 Hexagon Construction
This structure can only be used in symmetrical shapes.
Rule of Thirds
To use this construction it requires you to split up your painting into a 3 x 3 grid. Where the lines collides, that's where your'e focal points are.
The "L":
The "L" composition is used to get focal frames by creating a frame within a frame.
The Cross:
This composition is based on a cross, it requires your image to have different atmosphere on the different parts of your picture. For instance if at the top of your picture you have strong lighting and at the bottom half it's dark etc.
Iconic:
This composition is also called "The pay off" and relies on symmetry. It is pretty much simular to The Cross one but adds two diagonal lines to create the shapes of triangles.
Examples
Here I have chosen a poster from the game "Deus Ex: Human Revolution" and as you clearly can see that they use the iconic composition with the glass shards to attract your eyes to the main character in the middle. Some of the glass shards even fit precisely with the lines.
Here you can see a Concept piece from the game "Thief" where they clearly used the "L" composition. It is very common to use in Environment pieces like this to attract your eyes to specific key points.