Symmetry is the balance of elements of your painting around a central axis or point.
Both sides will usually match.
with symmetry you can achieve beauty through harmony and balance
If you arrange your picture to have mirror images of each other then you have produced a "inflexible symmetry"
Example: a painting of two people at a table having a meal.
If you have a painting with only similar
shapes exist, you have a "flexible symmetry"
Example: a still-life with numerous objects, all differing in shape and color
The "Golden Mean or Section"
This is a very common Greek principal in art.
The "Golden Mean" is accomplished by using a 3 to 5 ratio.
I could explain the complicated method of arriving at this but as an artist all you need to remember is:
Whenever you want to find the "Golden Mean" on your canvas, simply multiply the LENGTH or HEIGHT of you space by 0.6. This will give you the point of division without the complicated calculation.
Here is an example, if you draw a horizontal line running across the vertical line , you get the "golden Mean where the two lines intersect.
If you are designing your own pattern this is so helpful to know. Using this principal gives you a great composition
If you place your center of interest at this point you will have a very pleasing composition. The intersection of the two lines is the "Golden Mean" Try experimenting with this and also look at some of the great paintings that have been done, see if you can see how they placed their center of interest in the "Golden Mean" Move the horizontal line up or down and it will still show you the "Golden Mean" where the two lines intersect.