A balanced rendering is typically more aesthetically pleasing and harmonious than an unbalanced one, so before you start to render, take some time to plan your composition and think about where you want to position the visual weight in your render. Visual weight is an imaginary gravity that compels you to look at a particular subject. When a subject is highly compelling, it has a lot of visual weight; when you don't really notice something, it is little visual weight.
The main problem you run into when rendering subjects with a lot of visual weight is making sure they hold the viewer's eye disproportianatly, throwing off the balance in your rendering. For example, people in renderings automatically have a lot of visual weight, so you have to be careful how you render your people so as not to create unbalanced proportions of weight. When balance is absent from the rendering, the human eye tries to resolve the problem, and you certainly don't want your viewers to focus on fixing balanced problems rather than seeing the meaning you intended in your rendering.
To achieve balance, spread out the visual weight so that every part of your rendering attracts the eye. For example, if you notice that you aren't really looking at the top of your rendering, create a reason for the eye to go there. You could put something like an airplane or hot-air balloon in the sky, or you could use other objects in the rendering to create an eye path that gets the eye of the viewer to the sky. Something as simple as a steeple pointing to an empty expanse of the sky can give the sky visual weight. Don't worry if a single object has more visual weight than any other thing as long as you balance it with other objects that are still interesting enough to draw the eye. Whatever you do, keep it simple! Too many objects in a rendering tend to create overcrowding and disharmony.
Imagine that your rendering is a teeter-totter. If your subjects are the same size, you can balance then perfectly by putting them both the same distance from the center point. On the other hand, if your objects aren't the same size, arrange them asymmetrically. For example, you can balance a tiny object with a larger one if you place the smaller one far enough away from the larger one that your eyes naturally flow to both objects.
Without balance, your rendering may end up visually lopsided, so don't skip this element of composition as you plan for your next rendering project.