Closer is also always better for people as when you move further away you tend to lose the expression on their faces.
Here are a few ways that you can get in closer to fill the frame:
1. Use your camera's zoom
2. Physically get closer - you should never just stand in one place shooting away but rather move around and get different viewpoints including a closer one.
3. Crop your shots. If its not possible to zoom in anymore or get closer you can always crop your photo after so that it fills the frame.