The most used lesson in artistic composition is the rule of thirds. While there are lots of ways to compose pictures, this short cut always makes an image more interesting than most where the subject is dead center. If you're shooting a close up of a person's face or other object, putting it in the center is the thing to do. But, if you have a picture with a person in the center and lots of scenery around him or her - well, it could be improved.
Exercise: Take a piece of paper and draw two horizontal lines dividing the paper into thirds.
Draw two vertical lines again diving the paper into thirds.
Note the four places where lines intersect each other.
Now go take a picture of anything - placing the main subject at one of those four positions one third of the way from the top or bottom and one third of the way from the side. In fact, try placing the same subject at all four intersection positions. Take a look at the pictures.