Composition deals with the arrangement of pictorial elements in a picture. There are special books on this topic. I recommend that the reader finds some books on composition. Rough guidelines are given here.
A key factor of good composition is the balance. The objects depicted in a painting should keep a balance but a symmetrical composition is not preferable. There are many ways to achieve balance in composition.
As a rule, arrangement of objects along a curved line is preferable to that along a straight line. S-formed composition is often used in Western painting. In Chinese painting it is used too.