There are many ways to add emphasis to an artwork.
One way is through the use of color. When you consider the colors you are using, you should keep in mind that certain colors have more weight than others. For example, red is a powerful color and is often used to draw attention to something. If your piece has a lot of red in it, it might be a good idea to lessen the amount of red so that it doesn't draw too much attention away from other things in the piece.
Another way to create emphasis is through size and placement. If there are two objects of equal importance on your canvas and one is significantly larger than the other, that object will be more prominent than the smaller one. Also, objects closer to the center of an artwork tend to be more important than those farther away from it because they're closer to where viewers' eyes naturally go when they look at something new—which means that placing an important object near or on top of another one will make them seem even more significant together!