A good photo has to be a piece of art and contain a few important elements. It must create freshness, positivity and smile. There must be an attachment of beauty in it so that the impact is long lasting. It must reflect the personality of the photographer. There must be a message in it. It must be simple and eye catching. There has to be a plan in it and it must not have an error like faulty light, out of focus objects, half shadows, or something ugly. You are conveying a message and so it must be as decent as possible. There are many more issues and I feel there can be a set of guidelines for the beginners but finally we can see that the audience or viewers must love it.