Composition is the key. Never put something dead in the center. Think in diagonals. Different structures and composition lines. Dark versus light.
There is a lot to think about in the beginning. Later on it will go automatically. But I would first concentrate on composition. What is the subject. A classic in portrait pictures is to have one eye in the center, not the face. Have enough space around to let the subject breath. Experiment with holding the camera in different angles, slightly titled. Capture people when in motion. Action is attractive.