Many amateur photographers leave too much space around their subject when composing a shot. If the area within the frame is cluttered, it can be hard for the subject to stand out.
Don't be afraid to fill the frame by zooming in, moving in close, and even cropping part of the subject as our brains will automatically fill in the missing details, such as with the flower image below.
Filling the frame removes unwanted clutter and places greater emphasis on your subject. In extreme close ups and macro photography it can also capture small things that a wider shot can't do justice to.
Filling the frame is only one type of compositional tool, and is not ideal for every scenario, but it's a technique that can give a unique perspective to a simple subject, or highlight one aspect of a busy scene.
For example with architecture you could fill the frame with the building itself or zoom in on interesting features such as the entry or windows, to make a creative composition.
By zooming in, the lines of this quirky building in Prague can be seen in greater detail.
For portraits you can choose certain facial features to be the focal point or photograph from different angles keeping only the subject's face within the frame.
By having the a small part of the child's face take up most of the frame, the length of her lashes is elongated and enhanced in a beautiful way.
Taking lots of images using this technique can be a good way of telling a photographic story of a large scene, especially if the images are combined together in an album or collage.