So, start reading here: 10 Top Photography Composition Rules | PhotographyMad.com
Composition is something that should be done well also with a point&shoot camera, it's matter of choosing the subject and concentrating attention on it. In the first, you cut down two legs of the dog. All pictures are centered (read about rule of thirds), sometimes with disturbing objects on the background (a P&S makes it difficult to blur them, but you may always avoid to take backgrounds like the one in the girl pic). Comparing the first two you may also discover some white balance problem - same scene, same subject, different colors.
It's just the beginning .