When taking photographs of people there are several things to consider where composition is concerned. In this photography tip I shall concentrate on the close up.
Portraits usually look better if they are taken as close ups, concentrate on the head and shoulders. If you get in really close it does not matter if you crop off the top of their head, but it is usually better to not crop off the chin (there are always exceptions to the rule). Take a look at the example below, the 1st image is full length of 2 people:

Photograph of 2 people full length
The next image is the same picture but cropped to show just their head and shoulders, it has a much more intimate feel about it, you can see the detail of the faces and feel much closer to the people, more like you are there with them, rather than just looking at the at them.

Photograph of 2 people close up
Here is another example, the 1st image is of a baby full length, it is just a baby, you don’t get any feeling of being with the baby or any detail of the face:

Photograph of baby full length
The next photograph is really close to the baby and you really start to feel like you are there with the baby and get a feel of the mood she is in, it has much more impact. In fact it could even be cropped a bit to remove some of the forehead and the red top.

Photograph of baby close up